Embarassing question
I have had this, but it wasn't due to my fibro per se. It was from a sensitivity to caffeine and chocolate. The doctor told me to eliminate caffeine and watch the chocolate and within 2 weeks the pain was completely gone. Now, getting off caffeine caused me a horrible headache for 2 weeks but after that I was fine.
Another time I got this was from a drug reaction. I took zantac and it happened and one other drug I can't remember the name of. My brother had the same problem. Sometimes, these side effects aren't even recorded on the label.
Hope you get to the bottom of it.