Check your body alignment at your machine. Arms should be bent at a 45 degree at the elbow. Get a good chair with lumbar support and adjustment. Office supply stores have some good ones at a decent price. Another thing, move often. I have my ironing board on the opposite side of the room which forces me to get up and walk. These pains also happen to computer users. The body was made to move and work. The few seconds you loose by not pressing at the machine will pay back with feeling better in the long run.
I learned the hard way after an auto accident. We sew better when we feel better. Take care. :thumbup: