Pain under shoulderblades

I have a constant ache under both of my shoulderblades. It feels like a toothache and seems to worsen as the day goes on.
When I push on the muscle where it hurts, it feels like it is bruised.
I have been to a chiropracter for my lower back and have told her about my shoulders and she has “cracked” them before but it doesn’t seem to help.
What could cause them to ache like this?