Hello,
Have you have xrays or MRI of the cervical spine and thoracic spine?
These help to rule out other issues that can cause arm pain.

I'll post the useful sticky link for you-
http://neurotalk.psychcentral.com/showthread.php?t=84

If you have even had whiplash, concussion, or any upper body hit, fall or sport injury you might consider getting a evaluation by a expert chiropractor. If a head/neck hit maybe by one that specializes in the C1/C2 cervical adjustment.
sounds scary- but I have had it done and it is very gentle and painless.
the first post in the stickys has a section with chiro info sites.
Take the time to find a very expert and knowledgeable DC - but this applies to most anything anymore.....
My DC does PT type treatments also and is partners with a massage/PT therapist.