I Have This Fluid Filled Bump Thing On My Lower

I have this fluid filled bump thing on my lower butt cheek. It hardly hurts but it is fairly large (like finger tip sized). It's is clearly filled with fluid as it easily moves around and has lots of give to it. This is the second time this has happened and last time it leaked out some blood and other stuff, I covered it with a bandage as it drained, it formed a scab over it, and eventually went away. I was just wondering what it is and how I can remedy it?