Hi. Thanks for your query. Noted the history and understood your concerns. When the stool is black means malena and it is smelling like acid, this is indicative of a definite problem in the colon or ano-rectum. I would advise you the following in such a situation: Get the stool tests for three consecutive days. Tests of blood for CBC, diabetes, liver and thyroid functions. Ultrasonography of abdomen followed by CT scan if something is suspected. Colonoscopy and biopsy. If we get a definitive diagnosis during the course of investigations this can be picked up well and treated specifically to get you the results. If all the investigation are normal then only this an be said due to irritable bowel syndrome. Control of stress and anxiety is the mainstay of such a problem. Also identify the foods and beverages that cause such problems and stop these altogether. Have only boiled and cooled water and home-made fresh foods.