Have you had any really good PT or any expert chiropractic assessment?

Often MD's don't mention these options, I would think the dr would mention trying some PT ... But often a general PT or rookie PT is not familiar with TOS or complicated treatment protocols..
It could become a case of rush you though a strengthening plan - no matter if it helps you feel better or not..
If it is TOS that approach rarely works and usually can make you worse..

Any work, hobbies , sports, accidents that may have triggered this 4 yrs ago?
Sometimes it helps to look back to see if any specific or accumulated activity set it off.

Have you had x ray/MRIs of cervical spine ? To rule in/out any causes from there?