I know exactly what you mean about the pain. I also could not stand up and it was worse about an hour after eating. It didn't matter if I had a bowel moment, I still had the pain. It was awful. I have had pain in the same area for over a year. I have been on/and still am on Canasa (rectal med), 6MP, Colazal, and Fibercon. I have had every test on my gall bladder, Cat scan of my abdomen, x-rays, and also an MRA (MRI for my arteries going into my intestines). I have had UC for 19 years and this past year has been the worse for the pain.
After inconclusive tests, I was given Amitrityline (don't think this is spelled right) back in April. I started on 10 mg which helped for 2 months and then the pain came back and they changed it to 25mg (in June). I have been pain free since then. I am not even sure how it works but it did for me.