You should do colonscopy as soon as you can. You may have a polyp and if not taken care, it will turn to ....Is that enough to scare you. Make an appointment to your Gastroenterologist now!
I suggest that you type rectal bleeding into google and click on one of the many descriptive sites. The Medicinenet one is particularly informative.
This should prepare you for a discussion with a specialist G.I. doctor - always assuming that you have posted this question because you are suffering from blood ex rectum??
regards
Morecambe