Hello!
I would suggest you an X-ray of your shoulder joint and also a proper examination of your cervical spine area and your shoulder near an orthopedician to come to a diagnosis.
Till that time take pain killers intermittently and apply ice packs.
Take care!
Dear Top,
Did you find out what was wrong with your arm? I've had the same thing for a year, but my doctor can't figure it out. Please help me if you can. Thanks!