Have you tried physical therapy? My husband had about the same thing. They said he had an impingement of the muscle or something like that. He went through a series of exercises and as long as he does them periodically now he does not have many problems. I have about the same thing on the other arm, I am left handed so it is on the left side. I have started the exercises and it helps when I do them. I just need to remember to do them before I start in the sewing room!
The exercises strengthen the underlying muscles so they can overcome the impingement. They told him to use some inbuprophen for the inflamation while it was hurting so bad.
Phyllis