Most people should have little to no rectal pain after a routine colonoscopy. But it depends on what was done. If a large polyp was removed from the rectum, for example, then you might have rectal pain but it should not last more than a day or two. If you continue to have pain then you need to contact the doctor who performed the colonoscopy to let him/her know.

Weeks to months. If pain does not improve, reconsult GI. There is something called Post polypectomy syndrome that must be evaluated if polypectomy was performed.