Ovarian Cyst?

Okay, so last June I went to the emergency room because I was having pains in my lower left abdomen that were so severe I could hardly walk. I ended up doing a bunch of tests/talking with the doctor and a couple of nurses, and they all said they were sure that I had a cyst on my ovaries....well, the results came back negative? I was confused because I was truly in terrible pain and the doctor sort of brushed it off and prescribed my some hydros and told me I should be fine. Well I did some research and my symptoms were consistant with an ovarian cyst. Well it's been about 8 months later, and I'm having similar pain again, near the same area. (after the pain left the first time I hadn't experienced any more until about 4 days ago). It hurts to do anything super physical...it honestly hurts to roll over sometimes. I'm experiencing frequent urination and pain during bowel movements. I don't smoke, I'm not overweight, and I'm 24 years old and generally healthy. But now I'm stuck with a ton of medical bills and no answers....so i'm afraid to go back to the doctor and get the same results. But surely pain like this isn't normal? Is it possible for a cyst to not show up in an ultrasound?