As hard as this may be for some to believe, after having ate pizza from a particular pizzaria I soon found out it was the culprit of an intense bloating with a very unconfortable knot in the stomach feeling, this would go on well into the second day.  I might add that there has never been any foods I ate from anywhere since or before that that had this same effect on my stomach.  This happened every time I ate from there, about half a dozen times, and I refuse to ever eat from it again. My point, start paying attention to what you eat and try to figure it out on your own until you find a potential culprit.