My cousin was operated in his intestine a few years ago but it left a small bulge on his tummy like a protruding bump in the place where he was operated. now, his tummy always aches & vomit when he is eating much. is it because of his operation?

It sounds like he might have a hernia (an opening in the gut wall that allows parts of the intestines to bulge through- this can cause nausea and vomiting) This can be dangerous, because the intestine that bulges through might become trapped and if it swells the blood supply could be cut off. He should see a Dr to determine if the hernia needs an operation to close it up.