I have had a sore upper arm & round the back of the shoulder (non bc side) & have seen a physio at times. The one thing they have all said was about my posture. Now I don't walk around with my head down or anything like that but I dont keep my shoulders back & head high enough at times & it makes a huge difference. When I was away recently it played up & one of my friends massaged my back & down my arm & we iced it for a while, it was instant relief. The other thing I find that helps are the post surgery arm exercises the hospital gave me......I still have them after three years ......& use them !
I know physios are expensive, I go to the local uni health clinic where they have a student run clinic (final years) fully supervised by local physios & lecturers. Much cheaper at $20 or $30 depending on health or student cards.
Carmel