I'm glad your ovaries are okay.
The cat scan would have shown any tumors.
This may be an intestinal infection.
Your next step would be to see a GI doctor for further testing.
A colonoscopy may be in order.
It really depends on what infection is growing. It could be other things such as irritable bowel or a fungal infection which would need a different antibiotic.
Intestinal infection is only one of the possibilities. Without further testing, to guess which one would be purely speculation. You have pretty much ruled out the possibilitiy of ovarian cancer. A colonoscopy and blood work, possibly a stool speciman are in order next.
I wish you the best! please keep me posted.