I am not a Dr. nor in med field, however my step-daughter had this issue a couple of years ago after taking a round of antibiotics. I'm sorry, I don't remember the name of it, something that started with a "c", however I do remember that when the test came back we had to go in right away to get it treated. I suggest going to your doctor right away to be on the safe side.
Any time you see blood, or have a change in bowel movements, it warrants seeing your doctor just to be on the safe side.