If you haven't had any cervical spine x ray or MRI that might be the next step, to rule in/out any spinal issues, or any bone anomalies..
And/Or advanced PT evaluation or expert chiropractic evaluation..

Personally I had better care & faster results with a very good multi modality (soft tissue work and a mix of therapies used) chiropractor than with most of the PTs I had been to..

Post #1 on this sticky thread is a pretty much crash course on TOS and related conditions as well as treatments..
http://neurotalk.psychcentral.com/thread84.html

you can also try some things on this page for easy at home self care to see it it helps -
http://neurotalk.psychcentral.com/album.php?albumid=422