Rectal Bleeding

Ok, so here goes. Last year I had an episode of rectal bleeding (like covered the bowl, tp, etc) and immediately went to the doctor and had a colonoscopy. That came back fine except for two benign polyps and hemorrhoids. Anyway, after that I got what was likely an abscess (or maybe a thrombosed hemmie) which I popped (DO NOT EVER DO THIS) and it became a fistula. I had a seton put in the fistula in October. Everything has been going well for months and then in April I was totally constipated and strained a bunch so was not surprised when one morning I woke up to some blood on my undies and then during my morning constitutional. Everything fine until this last Saturday where I had blood on the tp after a rather easy movement. I am set to see the doctor in July, but wanted to ask whether the colonoscopy could have been wrong. I know I have hemmies and I know I have a fistula, but they have been really quiet. Do they just randomly decide, "Hey, I am still here...time to freak out?" And, if that is the case, at what point do you go back to the doctor for bleeding? I want to believe that the colonoscopy was done correctly and would have caught anything. I also do not want this to be another abscess. I mean are there people out there that know they have hemmies or a fissure or something that can cause bleeding and just pay no mind when it happens?