To answer your first question, it could be a virus, it also could be a variety of other things that cause it such as a simple fall or even a minor car accident. As of right now, there is no official cause for my fibromyalgia, I just have it. I am visiting my FM specialist later this month and I will ask about the latest and greatest on the research end and see what he says.
As the others have said a good rheumatologist is very helpful. I also go to a pain specialist to help with the muscle pain I get from it. Unfortunately medication can only go so far and right now most of us have to "live with" what the meds can't cover.