Help with my vigan ( even tho that sounds bad) HELPP!!?

ok I'm 17 and I'm not a virgin but I only had sex with 2 people, but even before I had sex I had white goop on my underpants. And lately it kinda smells. And I'm shitting my pants cause there is something wrong obvv, could it be a yeast infection ? And I dont think its a sti but what are something that come with sti ? Someone please tell me !! :(