Now usually my stomach going upset after i eat food from outside. but my firends doesnt happen anything by eating same food... what is the wrong with my stomach ????

Maybe the dairy?: As a pediatrician, I see my patients lose their ability to digest milk sugar (lactose) as they grow up. That is normal. Two-thirds of the Earth's population become lactose-intolerant. One can eat lactose-free versions of the same foods, or take a Lactaid tablet with the meal. An inability to properly digest oils and fats is a different problem. One's doctor can look for other problems too.