Chris,
Sorry to hear about your discomfort. It is an on going issue for fighters and non fighters alike. Also, a lot of men carry stress and trama in their upper to mid back, so that might also be part of it.
Your issue could be a number of different things. It is possible that you are having trouble with your Erector Spinae, Lats, Trapezius, Rhomboids Major/Minor), and/or Teres Major/Minor. It is also a possibility that you are having trouble with something totally different and it is just affecting your mid back. Everything in the body is connected.
That being said, I would need more specific info, but in any case I am a yoga teacher, not a doctor capable of giving you a specific diagnosis.
My advice is to definitely see a chiropractor regularly and also get regular massages. It helps a lot. Also, try a restorative yoga class, make sure they use props, and try and regularly go to yoga classes.
I could tell you a bunch of postures to help the mid back, but without being there, it would be dangerous to do so without the help of a teacher, or a DVD giving you specific instruction.
Rebel Yoga DVD's for fighters coming soon my man!