16 year old worried about colon cancer ! symptoms, abdominal pain for a week , on/off constipation for 5 months, blood in stool 2x in past 2 months?

Constipation: Colon cancer is extremely rare in a teenager. Your bloody stool is due to your constipation. You need a diet change where you introduce more fiber in your diet. See a dietician for help.

Unlikely, but...: Bleeding per rectum may originate in the anal canal, the rectum, or further up the line. Frequent anal sources of bleeding include hemorrhoids ; fissures, that may respond to modifying stool texture (fiber, softeners) and topical agents, or require further intervention. Similar bleeds can be seen with anal ; rectal cancer, infections, ischemic colitis, diverticular bleeds, inflammatory bowel, etc.

Thanks for asking: I am glad that you are concerned about your health at this age. You are having some things that suggest your GI system is not acting quite right. Pain, changes in stool and blood can be signs of colon cancer, but that is very rare at your age. Other conditions like inflammatory bowel disease (crohn's) are more common, but less serious most likely. Family history critical too. Since blood, be seen.

Workup: I hope that you have been seen. At your age there should be a screening test for inflammatory and autoimmune disease. It may be just a local irritation though. I would advise having a complete blood count and ESR test.