Ulceritis colitis can cause blood in the stool,alcohol abuse among other things get to your doctor they should perform a simple test where they will give you a stool testing kit which you will do at home and then return it for tests.
I have ulceritis colitis and there are becoming more and more cases of this every year but still the magical pill still has not been invented and still noone can tell you with hand on heart what causes it..

I found out it was just a hemmroid, I never had one before so I totally freaked out about it.