sweat down there (HELP)

I'm 15 and I go to school and walk alot and where I live is hot. now it's cold so I'm kinda worried about what's going on. during the day my vagina feels "wet" 24/7. literally one day it was so bad that when I got up from a seat you can tell something that was wet sat there. like it goes through my clothes now. I change my undies everyday like you're supposed to but it looks as if I keep them on for a week. they're covered in whiteness and like it gets chalky when it dries and when I get home I feel disgusting and embarrassed. I don't know what's wrong and was wondering if this happens with anyone else and if anything would help me? it smells like my underarms when I don't wear deodorant, and now that's it's cold and not so hot it's still going on so it's not so much because of how it's hot. but it worries me.