Red Blood In Stool, Dark Clots, No Pain, UTI, Intestinal Infection, Weakness, Dizziness. Taken Antibiotics. Is This Colon Cancer?

Hi, I am a healthy 20 year old woman who eats a mostly vegan diet. I have been passing large amounts of bright red blood in my stool with some very dark clot-like blood within the fecal matter. It has been 4 days of this and came on very suddenly with no pain. i am passing about 1/2 cup a day and i went to the ER on day 2. The visit was hurried and I still am feeing unclear. I also have a UTI which came with no symptoms at all. The ER told me i had a UTI and an intestinal infection that could be a number of things. I think this was brought on by going on a week long sugar binge after scarcely having ANY sugar/ processed foods in my diet for the last 3 months. Could this be colon cancer? I am feeling weak and dizzy when I stand. I am reluctantly taking two antibiotics and am more inclined to heal myself through diet and holistic remedies.