> I throw up and eventually pass out.
sounds like you might be having a vasovagal episode, Yana, which is brought about in your case by the stomach pain
get hold of a blood pressure monitor and note your blood pressure and heart rate when you have these episodes
If it is related to when you eat, you may want to get checked for a hiatal hernia. At 18 for you to be having heart problems, it would likely be a congenital heart issue. Doesn't sound cardiac. make a routine appt with your md, not necessarily an emergent one. Don't worry too much in the meantime. If it is a hiatal hernia, small frequent low fat non-spicy meals will help. Try it take care of yourself.
Could be air trapped or a stomach issue or even a pulled muscle. It is not a heart attack. I do not think that heart attacks would come and go like that. The symptoms would persist and worsen. They would not disappear and come at various moments.