I wouldn't panic. Your doctor is being thorough which is good. Obviously there has to be some reason for the pain. The only way to diagnose ovarian cancer is through a biopsy but if he saw no masses on the ovaries, I wouldn't worry about it.
If everything is ok, you might want to go to a gastroenterologist and look into the possibility of irritable bowel or something like that.
Just be glad that you will soon have answers. It could be anything, and most conditions are minor and benign.
I had what sounds like similar pain to you but when they did the ultrasound they found a cyst on my ovary. This pain lasted 5 months until my pain was 11/10 on their scale of 1-10 and I had to get surgery to remove it. My pain went undaignosed for about 3 months. If your ultrasound didn't show a cyst then I wouldn't think it would be any type of ovarian issue. From what I know ovarian cancer isn't just there without a cyst. Be patient and it is good to have a thorough doctor. Good luck!
IBS (Irritable Bowel Syndrome) can give the symptoms you describe. The ultrasound would have shown any problems with your ovaries and uterus. So now the Dr can look inside your uterus and see if anything is going on in there. Try not to worry until/unless they tell you something is definitely wrong! I know it's easier said than done when there's pain involved, but take some hot baths and try to relax.
Try upping your fiber on a permanent basis (prunes, benefiber, metamucil, etc) and increase your water intake and perhaps some of your pain will subside.