Possible diagnosis for dull ache between should blades for three months?

[Beeceemark]

Hi everyone. This is my first post and I am looking for some kindred folk who may have experienced what I am experiencing. I have had a dull ache between my shoulder blades (interscapular) for three months (since end of October), primarily on my dominant (right) side. I have taken very conservative treatment options (three visits to a physiotherapist in past three weeks and use of NSAIDs, such as Aleve on a sporadic basis) because I do not exhibit any of the warning (red flag) symptoms that should compel an immediate visit to a physician (no weakness or numbness, no fever, no swelling, no night sweats, no pain waking me at night, etc).  Also, my physician is 25 miles away in my former hometown, which makes it a bit more difficult to make the trip. I did go to a walk-in clinic in early December, as this all seemed to start with a mild bronchitis which caused a lot of coughing and subsequent intercostal rib ache along with corresponding ache in the upper back. I thought that with the cough getting better the ache would go away soon after, and that physician confirmed that he thought this was what was causing the problem and "not to worry".

Fast forward another 7 weeks or so, and the ache is pretty much there all the time. It is not enough to stop me from working or doing every-day tasks, and is not affected by movement, but I'm always thinking about it. The characteristics of this discomfort are the following - dull ache just below the scapula and primarily on the right side; ache that sometimes goes into the scapula and can refer to the middle of the back (spine) at times; ache is generally unaffected by movement, though there is corresponding stiffness; corresponding ache in right shoulder (started about a month ago, and compounded by my stupid decision to go to a rock climbing gym with my son); sometimes the ache goes into the upper right arm above the elbow (this only started a couple of weeks ago).

I find relief only with three things. 1. Moist heat (like the hot tub) is a saving grace; 2. Vigorous exercise; 3. Sleep. It is better when I am lying down, but pretty much there all the time when I am up and taking part in daily activities. I also do a fair amount of stretching and have done some yoga.

My physiotherapist, whom I have only started seeing three weeks ago thinks I have major muscle stress and trigger points, which might be the cause of the problem.  He says my upper back is "hard as a brick wall" and says that this has been going on for so long that it could be another 4-6 months before it is finally better. I do have an office-type job where I spend a lot of time sitting in meetings and in front of a computer monitor.  I have been trying to monitor posture and take regular breaks to walk around.  My physiotherapist says there is better movement each time he sees me, but that the pain or ache is always the last thing to go.  While I don't discount his professional opinion, and hope he is right (except for the lengthy healing process), I am wondering if I might have a nerve impingement thing going on (perhaps dorsal scapular syndrome or something like that), osteoarthritis, a disc problem, or something more ominous?!  

The ache has not been getting worse, but is not really improving. However, some days it does feel improved (after the first visit to the physio, I felt good relief for about three days). I have not yet had x-ray or CAT scan, but will do that soon if there is no noticeable improvement.

Any advice that you can offer is most appreciated.