Hey Flower Lady, I'm sorry you're going through this.
The fact that your colon looks red and inflamed means you likely have colitis in some form (ulcerative colitis or possibly Crohn's). Zelnorm I don't think is indicated in inflammatory bowel disease. If your doc is telling you your pain is functional, you should find a new doc. An inflamed bowel will certainly be painful!
As far as going through all this testing with no clear answers, I totally commiserate with you. I went down to the Mayo Clinic a couple months ago for my problem, the symptoms of which are chronic watery diarrhea, abdominal pain (sometimes extremely severe), low-grade fever, blood in my stool, rectal skin tags, canker sores...all classic symptoms of Crohn's disease and at first that was everyone's guess. I had plenty of tests; small bowel series showing narrowing in my small intestine as well, upper endoscopy showing gastric erosions, positive fecal occult blood and leukocyte tests. But my two colonoscopies were clear, as was a CT scan. The Mayo GIs acknowledged that these are not symptoms of IBS but thought it was some kind of post-infectious process after having a history of parasitic infections from Africa when I lived there for a few months. But there is little they are doing to help me other than pushing "more fiber, more fiber" (I take six tablets a day of it, plus probiotics, calcium, zinc, etc. all of which are supposed to bind you up). It's infuriating!