acahillies pain and surrounding areas

I’ve had foot problems since a child, I think a bit of everything except I’ve never had any achillies problems. until now! I am a Fitness instructor and I teach about 5 exercise classes a day plus I am in training for a marathon so I know that I do a lot on my feet probably too much but I have just bought a new pair of trainers which are exactly the same as my old ones, the reason for buying them was because my old ones had been so comfortable for the past 6 months. The trouble is a soon as I started to wear these new trainers it felt as if they were rubbing at my achillies tendon and either side, which surprised me because they are exactly the same cut as the old ones anyway my foot didn’t hurt at all when I took the trainers off so I just ssumed they needed some wearing in! I decided to wear my other trainers and another pair of lower cut running trainers I bought for the marathon until the bruising had gone and I could once again wear my trainers comfortably. But It a week later it is apparant that i’m may not just be suffering bruising! I am still in pain and can’t wear any shoes now as it seems that the pain is aggrevated by having something against my achilles as I move.
The funniest thing is that bare foot its like I have nothing wrong, there is no pain at all and to actuially get pain when I press it I have to press really hard and move my foot at the same time.Can anyone give me any ideas as to what this may be? I have not trained for 5 days now and the race is in two weeks and it doesn’t seem to be getting better. Many thanks