Being a medical student, i just want to put out there that there are a lot of misconceptions patients often have in regards to blood in stool. Firstly make sure that this is blood, and not just red coloured stool. If it's red coloured, then you shouldn't worry as this is directly correlated with your diet at the moment. You're probably eating a lot of red meat (beef, veal etc), and believe it or not, but that directly impacts the colour of your stool.
However if it's certain that it's blood, then i would suggest getting a Colonoscopy done ASAP as 90% of the time this means that you're diagnosed with colon cancer. If you're unsure, request the colonoscopy exam from your doctor even if he refuses (they refuse since its expensive).