diet, diet, diet.
and i don't mean, "go on a diet", i mean look at your diet (what you eat). what we put into our bodies directly affects what comes out of them. this is the single most important aspect of health & it is also the most overlooked.
it sounds like your experiencing some sort of biological imbalance. do you have a balanced diet: one based on whole grains, fresh vegetables, fruit & legumes? i suggest avoiding meat and dairy as much as possible.
you can also systematically map out which element(s) are contributing to your symptoms by categorically elliminating one food item at a time over a period of time.
personally though, that sounds like too much work, i would suggest avoiding the "SAD" (Standard American Diet) altogether & just focusing on getting plenty of whole grains, vegetables, fruits & legumes (& in that order too).
you never mentioned whether or not you wear deoderant. . ? i reccommend picking up a salt crystal (sold at most drugstores & health food stores if not in the grocery store), they last forever, work great, won't leave any residues & are all natural. PLUS, you can use em' everywhere if need be. by the end of the day i know whether or not i used mine (hopefully others don't).
also, can you shower after gym class?
one last thing to consider: good oral hygeine (i.e. flossing and brushing daily)