I know this sounds gross.. but..?

It is most likely something you ate or you could even be getting your period. I know a lot of girls that get gas before their period. You can buy over the counter gas x. Its just a pill that helps get rid of the gas. It even has a minty smell to it. So that kills two birds with one stone. lol Good luck and remember that you are human and that us humans have bodily functions like that. Its nothing abnormal. Good luck in school. lol