What Causes Pain In Rectum?

I am experiencing a tremendous amount of pain in my rectum. I am 3 weeks post take down, from my loop ileostomy. I had ulcerative colitis and my colon was removed in Nov. I have been w/o my bag 3 weeks. I am eating a very bland diet but my rectum is on fire and in a great deal of pain. I have tried warm baths, butt cream, baby wipes. I am scared to go to the bathroom because it burns. I have a follow up with my surgeon tomorrow. Could I have pouchitis, a fistula, cuffitis?? How do you tell?