Bright red in stool only on occasion?

I had blood in my stool for the first time about three years ago. I had spent the day at the beach, drinking beer, eating hamburgers, and swimming. I thought maybe the burgers weren't cooked all the way no big deal. When the pains in my stomach and the blood was no longer accompanied by stool I went to the emergency room. The doctor said it was probably from the "dirty" water at the beach, gave me some pills and sent me home. Over the years I have had bloody stool on occasion; I would say eight or nine times. The thing that concerns me most is that sometimes the blood is not accompanied by stool. It seems like diarrhea but when I go to the bathroom it is just bright red blood. Sometimes just drops, sometimes a lot. I do have stomach pains with this. It usually occurs at night and continues into the following day. The only trend I've noticed is it happens when I have been drinking. BUT it doesn't happen every time I drink. It does not seem to matter what I drink or how much that is why I am not sure if it is related or not. I do not drink everyday but I have certainly drank more than eight or nine time in the last three years. So here is my question, if there is bright red blood with or without stool and it only every once in a while, should I be worried about cancer, or is there a less... extreme explanation? I am uninsured and can not afford a doc. visit right now, I have done research but I don't understand the inconsistency of the blood.