If you see blood in your bottom while pooping what does it mean?

Blood in stool: It can mean several things from GI Inflammatory Bowel diseases, to serious medical conditions such as colon cancer, diverticular disease, to a simple hemorrhoid or laceration from a large stool, etc. At your age the hemorrhoid is more likely, but any blood in the stool needs to be clinically evaluated by the GI dr. to be safe. Best wishes.