Fibromyalgia is not a disease, it is a collection of loosely associated symptoms. Many things can cause these symptoms, including magnesium deficiency, hypothyroid, adrenal fatigue, Lyme/coinfections, etc. If I were you, I would ask for these other things to be ruled out first before accepting the diagnosis...but that's just my humble opinion.
When I was told I had Fibromyalgia (actually, I had Reflex Sympathetic Dystrophy/Complex Regional Pain Syndrome instead, but the doctor was...less than savvy...), I started to read about
it and discovered many interesting things about
what else could mimic the pain, stiffness and fatigue. Nutritional issues came up during my research, and so I started taking more magnesium -- the "fibro" went away shortly after. So was it a magnesium deficiency, or magnesium-responsive Fibro? I'll never know...I'm just glad the magnesium fixed the problem...wish Lyme was that easy to "cure," LOL!