Has your doctor ruled out ruptured discs or pinched nerves in the back. I have isolated pain such as you describe due tol ruptured discs.
I would suggest getting Bath Therapy (at drug store) and Pain A Trate Ointment. Last Night I had an episode where my right shoulder, Rotator cuff and Right hand ached so bad I woke up screaming in pain out of my sleep. I got rubbed down in Pain A Trate and the pain was gone in minutes! Pain A Trate is an ointment that may be obtained by calling 1 800 282 3000. You soak in the Bath Therapy, it is for Arthritis, Bursitis, Tendinitis and inflammatory diseases that cause pain. Good Luck. Hope this helps.