Thank you very much for the useful information Don.
The chronic bleeding per rectum you have is due to ulcerative colitis as diagnosed by the doctor after colonoscopy, but since recently, especially if you have noticed this yourself that the bleeding occurs only/or more when you exercise, then yes, we need to think of other problems as well that might be complicating the situation.
First, any physcial stress can make the bleeding from UC go worse --- one reason.
Hemorrhoides ---- very common cause for bleeding and usually you get the bleed from hemorrhoides whenever you strain/exercise.
Rectal prolapse can give you a bleed but only if the mucosa is infected and ulcerated (this is a very painful condition).
Angiodysplasia (abnormalities in the blood vessels) in the rectum can also be the cause.
Since you recently have a colonoscopy done, almost all these causes have been ruled out except rectal prolapse (which is there) and for that you need to see the surgeon (this may need surgical repair). I doubt that rectal prolapse is giving you the bleeding, but yes, it can give you rectal and abdominal discomfort.
Also your treatment for UC need to be intensified, you may need addition of steroids and other immune modulatory drugs as clinically the disease is still not in remission (you still have mucus and blood).
Until then, keep yourself adequately hydrated.
And there is no harm in getting a consultation with a surgeon to discuss repair of rectal prolapse, which may provide you a symptomatic relief from the pain.
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