What is the most common red flag for colon cancer , i have diahrrea and gas but cause i have gerd, no blood no weakness or fatigue?

There are none: As you are young, first consider your diet and try cutting out gluten (bread etc) and fatty meals (read food recipes on packages). Then discuss your family history for colon cancer with family members, and ask the age at which the person got colon cancer. There are families that get colon cancer in the under 30 age range. Colonoscopy and genetic testing can be done by your GI doctor.

Bleeding: Your symptoms sound more like digestive issues. Colon cancer is rare, although not unheard of, in a 24 year old. Bleeding, weight loss, family history, change in your stools are worrisome. Consider speaking with your doctor to discuss your concerns, since it is possible to have no symptoms.

Not really any: Some may argue that bleeding is the most common red flag, but it is a red flag that we work up for cancer. In reality, only 25% of colon cancers will present with bleeding. Otherwise, your physician will take your history into consideration and make a decision if a colonoscopy is warranted. You are young, so though it is absolutely possible for you to have colon cancer, it is still very low risk.