Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Colonoscopy is a tool that enables a doctor to see interior surface of the entire colon. It is used for screening (to check the presence of a disorder), diagnosis and treatment the disorders of the colon. Colonoscopy is used to evaluate conditions when a patient have rectal bleeding (occult or obvious), iron deficiency anemia in elderly, unexplained weight loss, abdominal pain, constipation or diarrhea which is not diagnosed with other methods. It is useful tool to diagnose or rule out colon inflammatory disorders (ulcerative colitis and Crohn’s disease), polyps, malignant (colorectal cancers) and benign colon conditions, diverticular disease or foreign bodies. It also used to treat a bleeding from colon, repairing stenotic lesions, removing polyps or foreign bodies. Furthermore, colonoscopy is used for the the surveillance after colorectal surgeries or high risk colon polyps and screening for colorectal cancers. I agree with your doctor as you should be evaluated with colonoscopy for unexplained diarrhea and constipation. Hope I have answered your query. Let me know if I can assist you further. Thank you.