A few minutes ago I thought I needed to have a bowel movement. Instead, it was just a gas build up. When I stood up and looked into the toilet, there was a fair amount of blood in the water and something dark in the bottom of the toilet. With a stick I was able to drag some of it to the edge of the water at the front of the toilet. It was coagulated blood. I estimated there was between a teaspoon and tablespoon of this material. I've been having rectal bleeding off and on for about three weeks, but nothing like this. I had proton beam prostate cancer treatment a little over a year ago. And I had diverticulitis about two years ago. My last colonoscopy was three or four years ago. What could be going on?