@247pain You have gotten a couple of possibilities here, and that is always good. What does your rheumatologist say? Have you kept any kind of a written journal, noting time of day/weather/activity when this happens?
I also have fibro, along with a few other issues. Sometimes a simple change in barometric pressure as weather systems change will do me in. Sometimes I feel pretty good and push myself, then pay the price the next few days. Sometimes eating the wrong-for-me foods will do it. It is definitely true that each person is different.
Are you near a teaching hospital of Mayo Clinic campus, where you can get a more thorough evaluation?