Real Bad Stomach aches?

Ok so Mostly everyday when im trying to go to sleep i get like shivers and my skin goes spiky (goosebumps) then my stomach hurts really bad. i dont know why this happens? and after like about 4 mins i get shivers again and everything goes to normal. im a boy so its not a period or anything. i never eat over 7:30PM cuz i go to bed at 9PM. whats happened?