What Causes Rectal Bleeding?

Sir, myself Shankar 39 year having problem of rectal bleeding for past few days... rectal bleeding starded for two day and stopped itself without any medication.... Earlier in 2005 i had a surgery for anal fissure... but it reoccured... but now without any pain rectal bleeding occured and stopped itself... my stool is not in colou and shape since from 3-4 months... burning sensation in lower abdomen with pain and cramps in lower abdomen