For some reason your body is not digesting the fats/oils and proteins so your intestinal bacteria are doing the digesting and producing the smell and gas. An intermittant diarrhea may have caused some intestinal bleeding - red blood from the lower intestine or dark gooey stools or 'coffe ground' granules in your feces from higher up. Your Dr can order stool cultures which might show a toxin producing bacteria but people here seem to favor the Metametrix Lab intestinal panel which uses molecular methods to id the organisms and parasites in the gut.
Some herbs such as turmeric which stops the growth of some toxin producing bacteria, hot peppers and other spicy spices may give you some relief. You want to find as much as possible about the cause as soon as possible as you are at high risk for complications.