This study suggested that insulin resistance from chronically high blood sugar may help drive fibromyalgia. 

It found that treating the insulin resistance with the drug Metformin reduced pain levels.  The study was later retracted, but not for any problems with the findings or conclusion.  It was retracted because the authors didn’t follow proper procedures to obtain ethics approval and permission to use medical records.  Shame on the authors, but I’m still interested in their hypothesis:  That high blood sugar can cause insulin resistance and damage to small blood vessels in the brain, causing widespread pain.  If they are correct, in addition to medicines for blood sugar control, lifestyle changes to reduce insulin resistance may help.  This would mostly mean reducing the intake of carbohydrates, especially processed or high-glycemic carbohydrates.