Definitely sounds like ovarian cyst pain, I'm amazed you put up with it this long. Hasn't your doctor done *anything,* like put you on the pill to try to shrink it? I'd go see him tomorrow effing morning and say you absolutely need to have this dealt with.
That sounds very much like the pain I had for about 6 months. I had surgery in May to remove two cysts. The pain is not completely gone yet, but it is much, much better. In fact, I just had an almost pain-free period and am hoping that's the way they are from here on out.