I just had a bowl movement, it was not painful. But my lower stomach cramped up a little. When wiping I noticed a large amount of dark and bright red blood. There was also a dark red, bloody, fleshy substance in the stool. What could this be, and should I seek medical attention? (I have also recently, three months ago, had a colonoscopy and they removed a polyp. I am an 18 year old female.)