Went to the ER, now I'm confused?

I asked a question earlier about whether or not to go to the emergency room for my severe abdominal pain. I took all of your advice and went (thank you!).

After over 7 hours there, and after an abdominal, pelvic and trans-vaginal ultrasound, the doctors sent me home because they don’t really know what’s causing my pain. The doctor who looked over my ultrasound said my appendix looks okay, but there’s a small amount of fluid, which could be water or blood, in my abdomen/pelvis. He said this may or may not be caused by an ovarian cyst. He said come back in if you’re still in pain in a few days.

….. real helpful.

I am still in pain. Mind you, it’s not as severe as it has been. Any ideas on what could be causing the “fluid”? I am making an appointment to follow up with my family doctor.