I'm really puzzled right now. I recently finished a course of Flagyl for what my gi doctor suspected was giardia since I was having diarrhea, stomach pains, and nausea. So today, I had a plain hamburger with some ketchup and cheetos, and my diarrhea came back for about 2 hours. I'm trying to figure out why this happened. Could it be something about the food I ate, or is there another issue I might be dealing with?