Could Bruising In The Upper Buttock Area Be Related To Kidney Or Liver Problem?

48 yo F. 200 pounds, 5 '1". I was Diagnosed with Fibromyalgia/ CFS in 2003. I have noticed that I have frequent "bruising" in my upper left toward the middle of my upper buttock. It occurs in the same place about every 3 weeks or so, and I have not injured myself. What could it be a symptom of? Could it be related to kidney, liver problems, or a sign of dehydration.