I had that a few years ago. I had been trying out some of my old gymnastic moves (something that's not recommended if you've been out of gymnastics for over 10 years) and the next day I had a sore back. It felt a lot like a relly bad pulled muscle. Then the right side of my abdomen was really sore, but I thought that was just from holding myself so stiff so my back wouldn't hurt. I finally went to the doctor when I had a fever and was so tired I could barely get out of bed. Turned out it was a kidney infection. The pain was the worst I've ever experienced. I was on antibiotics for 2 weeks to clear it up.
Hope you're feeling better soon!
-female - 32 -diagnosed June 2006
-last 25cm of colon affected
-Salofalk enemas stopped working
-xylocaine enemas put me in remission
-Asacol 2 800mg pills 2x/day
-budesonide enemas as needed