Have you been given prednisone for inflammation? It really sounds like something is obstructing your pouch in some way, either inflammation or a stricture/prolapse. Have you had a scope to look inside your pouch for structural issues? You might want to ask for a defecography study to see if you have trouble emptying your pouch correctly.
In the meantime, definitely get a catheter if you are comfortable trying it. They suck but they are MUCH better than being in pain like you are describing.
Marlen Ostomy Straight Catheter 30Fr, 15" L, Medium. And a 50-60 cc catheter tip syringe. Plus some surgical lube. You need the syringe to clean the catheter, if your stool is firm, or if you ate anything chunky. You can get the catheter from a medical supply store online and the syringe almost anywhere. As long as you don't jab it in and ignore your body, I don't think it can hurt you. My doctors told me to get one without any instructions 