I found a triangular black bruise at the base of my spine /top of/middle of my buttocks . There is no pain at the immediate area, but my lower back (gluteus media area) on right side has had an aggravated nerve pain for several weeks that I had attribute to strain from recent household move. Not sure of thd bruise origin and concerned there may be physical damage now.what else could the bruise cause be, if there was no impact trauma?