You might want to go to the doctor and get checked out, as it may be that you already have some arthritis and the quilting is aggravating it. I also wonder if it could be carpal tunnel syndrome acting up.
You might also want to try quilting standing up. When I quilted on my domestic machine, I would place it on my cutting table. This was much easier on my neck and back, and it also changes the angle for the shoulders, wrists and hands.