I get random severe stomach aches.. i dont know what's wrong. help.?!?

it has been going on for maybe almost 2 years now. it happens like once a month or once every few months... i get horrible, horrible stomach aches. it is the worst pain i have ever felt. i get really bad sharp pains and then it also feels like a gremlin is inside punching through my stomach.. i dont know how to explain it but it's horrible. i had this stomach ache on sunday and laid on the couch all day, i have the stomach ache all day but then it goes away around 9:00 or 10:00 at night... i never eat anything when i have the stomach ache because it doesn't help and it makes it worse. i have no idea what it is, and it's really strange. i get it like one day out of the month and then it stays the whole day and then it just goes away.. but it takes me a couple days for me to get my appetite back after not eating.. but someone help.! i need to know what it is.! :(