hey,
I kind of went through that a couple of years back, got something similar and had to stop for a while. Now I am not sure how you got to your state, etc. But here is some rough advice from my experience. make sure you fully rest for a long time, and minimize computer(ergonomic keyboards, etc. help) and piano. you'll be surprised by damage you can do by just playing 30 minutes a day of piano, especially when you can't relax because of pain. Keep doing therapy, and try targeting neck/back, since the nerves going to the arm are all rooted there. (try working on your posture too) And you'll find practising in your head, Although difficult to do, is really good and useful at the end of the day. Good luck with getting better, and don't forget the most important thing is rest.