could it be stones?

My boy, 8, is having terrible tummy pain(naval area and below) he says it feels "hot". He has no fever, he's vomited several times following these pain attacks. Could this be caused by his eating something, he did popcorn, or could this be a problem with his liver or gallbladder? It seems he gets this sometimes, but we can never tie it in with what he's eaten or the flu or something. Just wondering what you all might think? Thank You all! Tweet