Chest pains

Hi, im hoping someone will be able to answer this question for me, bit of a long one, but im desperate to get some answers.

Basically, i am a lorry driver and do supermarket deliveries, as in 44 foot trailer full of 40 roll cages packed with food, as you can imagine, these are quite heavy, especially when it comes to the frozen foods. Anyway, i have only been doing this job since May last year, before that, i was a office bound pen pusher, and ill be the first to admit, completely unfit, no exercise for aslong as i can remeber and slightly overweight.
When i started this job, to begin with it was a bit of a struggle, used to ache for hours the next day, but soon it seemed to get easier and easier, until one day, i had a very tight chest, it felt like someone had there hand on my chest and was putting presure on it, this would come and go for sometime and i let it go on for weeks.
Then it got so bad, i decided to go to the doctors, explained to him what i did for a living etc etc at first he thought it was a bit of indegestion, not wanting to question his judgement, i took his advice and got some indegestion tablets, these had no effect on the pain at all, it seemed to be easing up so i forgot about it and got on with things, the pain was not so bad that i needed pain killers, but it was just like a dull ache now and again.
Anyway, one day whilst out, it got quite bad, just felt very tight, so worried i went into local casualty unit, they did a ECG just to be sure and had a listen to my chest and couldnt see anything wrong, the pain was easing up and they said to go back to my GP.
Anyway, again the pain disapeared for a while, so i forgot about it, still doing my night deliverys, and getting used to lugging this heavy cages about.
Then one day after waking up, i was in the kitchen making a piece of toast, doing nothing more than just buttering the toast, when i had a very sharp pain in my chest, right in the middle where the sternum pokes up, it lasted for no more than a second, and then i felt it in my back in the same place, then disapeard.
I was a bit shocked and didnt know what to make of it, so just forgot it, few weeks later howver, i had it again, it generally happens when i get up, when your body needs a good stretching etc.
This time, i decided to go back to the doctors again wanting some answers as this had been going on long enough and im beginning to get anxious about it all.
This time i saw a different doctor, he decided to have a poke around on my back, he commented on some of the bones in my spine in the middle, felt a bit tight and didnt seem to have much movement, he told me that basically, he thought that maybe i was trapping a nerve which is what the pain was, he gave me a list of exercises to do every day to try and get some more movement in my back and sent me on my way.
I left the surgery, still feeling a bit concerned and didnt feel like id been given the answers i want, i just want somone to say, “oh yeh had that before its such and such” but no such luck.
I decided then, that if he thought it was my bakc then i would go to see a chiropracter.
So off i went and found one, told her the whole story, and she had a poke around my back.
She confirmed that there wasnt as much movemtn in the middle of my back as there should be, and that muscles are connected to ribs from the back etc and this could explain the pain .
Im a big lad, quite broad and tall, and my natural position when sat is slouching forward, so this could explain the back problems, but the pain in the back was bearable, its this sharp chest pain i want to sort out.
Still no definate answers…
So on her advice decided to go along for some treatment, which consisted of a bit of massaging, bit of prodding and pushing, and alot of money.
This was making no difference to the pain, and it was happening more and more often, it was busy at work leading up to christmas and i was working long hours for the money, so was doing sometimes 2 shops a night, plus taking all the emptys back, i was shifting alot of cages.
The one thing that made me think it wasnt muscles, is that there was no way i could trigger the pain, by doing all of the exercise i have been given, no matter what position i get into, or how much weight i lift, i could not trigger it, it would just come at random.
A friend of mine suggested that i should go back to the doctor again, and ask to be refered for some physio.
So i did, this time while i was there, they did another ECG and blood test, all was clear, and put me forward for some physio.
This was just after christmas, and he said it was busy and i may have to wait a few weeks, i didnt bother me as this has been going on for months now a couple more weeks wasnt going to hurt.
So i was waiting for my appointment, 2 weeks went by, and no pain, weird i thought, it had gone away.
I had a call from the physio, and they booked me in last tuesday, it had been nearly 3 or 4 weeks now and i hadnt had anything, no back pain, no sharp chest pain, no aching, nothing at all.
I worked the saturday before, and was thinking that if i hadnt had it by the monday then id ring and cancel tuesday appointment with physio.
You guessed it, after a long saturday night starting at 18.00, by 6am my chest was feeling a bit “twingy”, no sharp pain yet, just felt a bit tight and fragile.
So i slept it off, woke up feeling a bit tight as i do most of the time after a good kip, but no pain.
I decided tho, i would go to the physio, so along i went, explained the whole story to the women, and explained how its a random pain, nothing triggers it in particular, although i have noticed it that when i pick my one year old son up, i get it then, and once i sneezed hard and that made it happen.

Anyway, physio had a poke, said same about back, but was mystified about this sharp chest pain, saying that if we get my back moving better then it might all come good!
Im fed up with docs, physio, chiropracters telling me that i have bones that dont move aswell in my back as the rest, its not my bloody back that hurts, its this sharp pain in the middle of my chest!
Again since that saturday night, ive had no signs of it reappearing at all, that was until yesterday
On friday night, i did a shop delivery, since christmas work has died off a bit, so we tend to take our time to make the job last longer to get more hours, but this night i wanted to get home early so when i got to the shop, i went into overdrive, i was pulling and pushing cages left right and centre, two at a time really going for it to get the delivery done, by the end of it i wsa knackered, but no pain, thought i got away with that one, that was until i woke up yesterday, i felt really tight in the chest and fragile, and i just knew, i could sense if it was going to happen.
I came down stairs, feeling fragile and just woken up , i sat down for a while waiting for my body to wake up.
My son was plaing in the lounge, i stood up, and decided to pick him up for a cuddle, big mistake, sharp pain in my chest, then into my back, so put him down rather quickly.
Now i knew id done it, it was hurting and my back felt sore.
As i woke up more, it felt like it was a bit easier, and off i went to work at 18.00 saturday, knowing full well id be doing a shop delivery that night and wasnt looking forward to it, got to work and so far so good, then as i went to climb into the cab, i had it again
Anyway, basically, i have had it again today, ive picked my son up a couple of times, and have felt this twingey pain in my chest, most friends and the mrs think i have done some muscle damage, having a young son and life looking good, i have a over imaganative mind and keep thinking i have something seriously wrong with me.
No one can seem to give me a straight answer to my problem, ive had a look around on the net and read about chest muscle strain, and wonder if thats what it is?

My problem is, thats its my full time job delivering to supermarket, so im doing
this 5 nights a week, and the advice ive read on healing a strained muscle is to rest it, this isnt possible with my current job, so im thinking of even changing jobs and just doing trunking work (just take a trailer to a depot, swap trailers and bakc, no physical work involved) but i dont know how long this will go on for, or if it will ever go away.
It feels like a muscle type pain, but then im no expert and havent had many muscle pains in the past, could it be tendons?
I dont know, so anyone that can give me some advice i would greatly appreciate it, as im beginning to get very anxious over this.
I know its not a sporing injury but thought prehaps you guys have had similar things or know of people with similar things.
I have no other symptoms at all, no weight loss, no change in my diet, nothing, just this stupid pain which is driving me bonkers