Re: Not sure what's going on...
I also had a fissure when I was young, I was only 20. The blood was bright red and sometimes made a distinct streak on the poops. I'm not sure what color it is if you have bleeding from farther up in the colon, I doubt it's so bright but I could be wrong. Did you already have a sigmoidoscopy or colonoscopy to diagnose the fissure? If not, it would probably be a good thing to do, just to make sure that's where the blood is coming from.
My nephew has full-blown Crohns. It developed in his teens. Nobody else in our family has Crohns, though I have always had issues, alternating constipation and diarrhea, periodic cramping, too much gas. (I am not surprised that I now have diverticular disease.) Chances are you don't have Crohns, but it's a possibility. Or you could have IBS. If it's one of these kinds of diseases it might take a while to diagnose. Again, the best thing to do while you are waiting to see the doctor or waiting for results is be really good to your body. Definitely drink more water and increase your fiber (but don't overdo), these are great habits to develop even if it doesn't solve your problems. Especially during your constipated periods eat foods that help you go more, for me it's certain fruits like oranges and strawberries.
Best of luck to you!!