I hate those types of sicknesses so much, seriously x.x
It could be a whole range of things, it's likely just to be some Gastroenteritis (A stomach bug). If it is, then yes it sucks and it's really bad, but the good news is it doesn't last very long, so you might be ok. If you haven't been experiencing vomiting, diarrhea or any of that other stuff, then it might simply be just a bit of indigestion, that can last quite a long time and can also be quite painful (It could also explain why your heart hurts, I've had that effect too when I experience indigestion). If it lasts more than 3 days, I would see a doctor about it.
EDIT: Of course another solution could be, as your mum suggested, gas pains. If you've started recently eating new foods, you may have an intolerance to one, or maybe you've (for example) eaten too much fiber, eating fiber rich food while not being used to said food can cause gas pains. I'm not a doctor and have absolutely no medical training, but here's just some suggestions.