Possibly extreme constipation. I had what I thought was appendicitis a few weeks ago. A constant, non-fluctuating, un-moving pain in my lower right abdomen. It lasted for about 5 hours and then I was able to get to sleep. It didn't hurt in the morning, but my muscles were sore from the cramping it caused for about a week after. I never figured out exactly what it was, but I think it might have been constipation, heh.