I have been blood tested, urine tested, x-rayed, ultrasound scanned, and had my abdomen prodded by five different doctors and three radiologists.
The ovary I had taken out has not magically regrown, and nor are there any bits of it remaining. There are no swabs or rolexes. I don't have any abnormal growths. My kidneys, pancreas, spleen, liver, bladder, and various other organs have all been examined and none of them found wanting. My contraceptive coil hasn't pierced my uterus. I don't appear to have diverticulitis. The only other tests they can now do involve barium meals (which might be an option if they thought it was diverticulitis, but as they don't it seems a bit pointless) or exploratory surgery.
The most likely explanation is surgical adhesion from when I had my ovary out. If it IS that then exploratory surgery would probably find it but they might not be able to do anything about it, and given that I am not actually screaming in agony at all times it's probably not worth it right now.
So I have to talk to my GP about pain management, pay attention to my stools (YAY! Funtimes!) and take lots of painkillers. Potentially forever. And go back if the pain gets markedly worse or I start having constipation, diahorrhea or vomiting and they'll do the exploratory surgery.
On the plus side I also now have written proof that I have not got dementia and my cognitive abilities are not suspicious. Yay. Witness my face of utter joy.