Since you mention some signs of carpal tunnel and you say you sit a lot at work- computer/desk job?
How's your overall posture - head forward, shoulders rolled or hunched?

Could be one thing or could be 2 things that happen to show up at the same time...

You might read some of our useful sticky threads on the Thoracic outlet syndrome forum- we call it TOS for short - can occur from chronic repetitive injuries. computer, desk, whiplash, sports type hits or falls.
http://neurotalk.psychcentral.com/thread84.html

Personally if the MDs can't seem to help narrow it down.... locate an expert chiropractor or advance PT person and get a comprehensive evaluation from them. See what they come up with...