I second that... given the fact that you are having bleeding alone warrants a colonoscopy. If you are constipated for a while, there is a good chance that you have a motility issue, and may also have a polyp/s that get irritated together with the wall of the colon and cause bleeding-- either from the wall itself, or possibly a polyp/s.
In any event, it is irrelevant how many times you have had bleeding... you have had it, and that requires further investigation.
In your case, it does sound like a motility or IBS situation. But the possibility for a polyp/s (benign or malignant--cancer) exists, so the sooner caught the better the prognosis. I don't tell you this to scare you, rather to inform you so that together you can make a decision with your Gastroenterologist whether to have a colonoscopy.
Personally, I would go for one in a heartbeat... the biggest pain is the prep. Really it's a small sacrifice to pay (having diarrhea and I guess also the bother of being groggy for a day, having a small stick for an IV for drugs that make you relax, sleep, mostly forget the experience, and feel little or no discomfort). A REALLY small price to pay for the peace of mind of knowing that it's nothing serious and that things can be done to ease your discomfort. Worst case scenario, if it is serious, it truly is best to know NOW rather than later so that it can be caught hopefully in its earliest stages before too much intervention is needed.
Best of luck and please keep us posted.