I'm not sure if my issue is exactly the same but I wanted to post to maybe ease your mind a little.
Last January (2013), I started to get pain in my lower right abdomen. It would be in my lower right abdomen and radiate around to my back and even down into my thigh. It would come and go and some months would be worse than others. I went to see my primary physician who pushed around on that area and couldn't feel anything and I had no pain either when they did that. However, the aching pain would still continue. I was thoroughly convinced that I had ovarian cancer. No doubt in my mind. My primary finally suggested I go for an external u/s of my abdomen to check out all of my organs inside as well as an internal u/s to check out the uterus/ovaries. I did both. Amazingly, everything came back normal. I was in complete shock. Would you believe after I got that news the pain disappeared? I haven't had any pain since the u/s results came back.
What does your doctor say about your fear of having ovarian cancer? I agree with other posters that after all of the tests you've had done, something would have shown up by now. The discomfort you are feeling could very well be simply hormonal.
Do you notice it more at different times of the month or is it just every day?
I know how scared you must feel because I was terrified and Googled constantly. Just know that odds are it's something other than what you think and most likely nothing at all. I think, too, that sometimes the more you focus on something and think about it, the pain will continue.