Gracious what an ordeal! It’s giving me flashbacks.
Last year I went through months of GI drama culminating in c-diff. But even after treating that, the diarrhea persisted. My GI ordered random colon biopsies to rule out microscopic colitis (so called because it can only be confirmed under microscope). And in fact that is what I have. There are two main types and I have collagenous colitis. I completed a few months of a colon-specific steroid that put me in remission. But i learned the most likely root cause was a medication trigger - notably including NSAIDs, PPIs, SSRIs, and some statins. You might ask your GI doc whether it makes sense to rule it out with a biopsy during your colonoscopy.

I hope you nail it down and get some relief soon.