My best guess would be cuffitis, but anything that erodes into a small blood vessel can do this. Have you had a pouchoscopy? Once treatments aren’t working then it’s especially important to reconsider the diagnosis.
There’s a good chance that you’ll be fine until your GI appointment. If the bleeding recurs in quantity then that changes, of course. The ER is likely to be a very disappointing experience unless you’re experiencing life-threatening bleeding.
Why do you think your doctor will overlook this? Do you need a better doctor?