I woke up with a burning sensation on the rectum and a small pea like sore on the side of my rectum. what could this be and how do i treat it?

Infection? Fissure?: Anal ulcers have several possible causes. Depending on sexual lifestyle and STD risk, syphilis and herpes are possoble. Anal fissuure, perhap infected. Anal or perirectal abscess. Severe yeast infection (thrush). And others. No way to know best treatment without professional examination and testing; you should see a doctor or clinic. Good luck.