You'll probably find it is a corpus luteum cyst and they won't do much more than keep an eye on it. Basically what happens is when the egg pops, the place it came from remains open for a little while and then closes up by itself. Sometimes it can take a little longer to close up and some fluid remains in it. That's what causes the pain. Usually they resolve by themselves over time.

Hope it is something as normal and common as this. Good luck.

Lisa