Okay. It turns out that proctitis is not the main problem—late in January, I'll need a colonoscopy to have a polyp removed. With some reading, I've discovered that such polyps are far from uncommon. Over 60% of people over age 60 get them, for instance. It is less common in people like me under 40, but no big surprise either.
I still resent it, of course. Somehow—and this is irrational, I know—I subconsciously think that because I have diabetes, I should get a pass on other unrelated conditions, like gastrointestinal polyps. But then I have varicose veins too, so that idea went out the window a long time ago. Health and probability don't work that way.