Severe Pain In Lower Spine. Why Am I Lethargic? Why Is There Mucus Discharge From Anus?

2 weeks ago I had severe pain by lower spine of middle of back that turned into a belt of pain around my whole lower torso section. Along with this was a fever, hot and cold chills, listlessness, reduction in body strength lethargy, constant feeling of the need for a bowel movement which only was water, and mucus with tinge of blood. It took over a week and a half to start clearing up. I was just starting to pass rather normal bowels and having my strength back 3 days ago, and now it s like the whole thing started up again - so far a bit milder with just the back pain and small mucus discharge from anus with blood tinge at times. I can t be up and walking for more that a few minutes before I have to sit on the toilet again and sometimes unable to stop the rectal discharge and am wearing a sanitary pad. What can cause these symptoms? When I saw a Dr. for the first bout he mumbled something about gastro ...... and I took stomach xrays(came out ok) and blood work(said low in potassium ); and he said to drink Gatoraid and take Pepto Mismol.