My fiance has swelling and pain on his right side by his ribs and has had and upset stomach for the last couple of days. what would be causing this?

Possible gallstones?: Usually pain on upper right side of stomach especially after a meal could be caused a gallbladder infection( cholecystitis) especially if the pain is severe and in some cases accompanied by fever and vomiting. There are other reasons that might cause pain in this area of the abdomen as well but this would be one of my first impressions and that requires immediate evaluation.