I have had fibromyalgia for years. My doctors prescribed medications, biofeedback, a tens unit, etc.
I found that mild, simple exercise (like walking) helped more than anything else.
Make sure you have a chair that is ergonomically correct for you. That is very important.
Watch your posture when you sew. Don't sew with your shoulders hunched over. Try to remember to keep those shoulders back.
Get up frequently and move around. I have less pain if I have to get up and walk to the ironing board to press some seams, that if I set up a small ironing station next to my sewing machine and and do all my pressing there.
Blessings,
Judith