Hi Idealist.
Well, the best way to describe FM is like this. At certain times the pain will drift. It does not have to be in all 4 quadrants at the same time, all the time. For example, my left hip and left shoulder are constantly in pain, but I rarely have problems with my right hip. My right shoulder does flare up occasionally. Don't forget that the quadrants also apply to the front so you could have pain in the front and not the back.
So, yes it could be FM but watch the pain for a little while and if you can't deal with it anymore, see your doc.
I hope this helped.