Since no one knows what fibromyalgia is, let alone what causes it, it's impossible to say. Antibiotics, however, destroy the good bacteria in the intestinal tract, and many in the natural med world believe overuse of antibiotics, even when necessary, is one cause of fibromyalgia. Food intolerances are also felt to be culprits. Sleep deprivation or bad sleep is felt to be a potential cause. Or maybe these are catalysts, rather than pure causes.