Some of the co-existing conditions of Fibromyalgia also include:
Chronic fatigue syndrome
Depression
Endometriosis
Headaches
Irritable bowel disease
Hypothyroidism
Lupus
Osteoarthritis
Post-traumatic stress disorder
Restless Leg Syndrome
There is also some talk about whether there is a chronic, subclinical (not a full blown) yeast infection component of Fibromyalgia. People who consume lots of sugary foods (sugar, fructose, and corn syrup) are more prone to yeast infections. Yeast infections can reduce your energy, make PMS worse, and alter your digestion habits.
I also believe that there may be either thyroid and/or estrogen-progesterone imbalances that are present, but which may not be severe enough to show up on lab tests as below normal values. They sometimes show as low normals. These imbalances may be causes or simply aggravating factors.