The main reason people get stomach aches when they are hungover is because drinking a lot of alcohol raises the level of acid in your stomach. To cure this, you need to soak up the acid. Eating something dry like plain toast (nothing on it) or saltine crackers. I know you don't want to eat anything because you don't want to vomit, but these foods are not tough on your stomach, so you shouldn't have to throw up. If you do throw up, it's not all bad because vomiting can help you cure your stomach ache. Also, to avoid a hangover, try to drink lots of water before you go to sleep the night you were drinking.