It sounds like the one thing that worked is Bactrim, but the effect stopped when the antibiotic was stopped. I don’t know about long-term Bactrim, but as SteveG has suggested, why not try Cipro (or Cipro + Flagyl)? Even if the effect doesn’t last most people can stay on them long-term. I’ve been on Cipro for about 15 years.
Pouchitis (or at least things that act like pouchitis) aren’t always visible on pouchoscopy.