If the doctors can't find an obvious cause for pain & symptoms, it might be good to do some reading about Thoracic Outlet Syndrome/Brachial Plexopathy.

Here's a thread that should be very helpful-
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http://neurotalk.psychcentral.com/thread84.html

this upper c spine info might be helpfull too since you mention a head/neck injury -
http://www.upcspine.com/self.htm