Welcome at HCM.
I have read complete details of your questions.
It looks from your details that you are having pain at back side of your shoulder.You are also having pain at different parts of arm.
Such type of problem can be there due to following reasons-
-Shoulder problems like impingement syndrome
You should consult to a orthopedic doctor for complete evaluation.
You should have a x ray of cervical spine
Take a good analgesic
like advil or ultracet
on prescription of your doctor.
If you have any other question then please let me know.
With best wishes.