I'm pretty sure I have a yeast infection... ? SERIOUS ANSWERS ONLY?

So I've never had sex but about a week ago I was sitting on this guys dick without a condom or anything and it had full contact with the outside of my vagina. He said he didn't have any STDs and that he'd recently been tested but it's not like he's gonna come out and say, "I'm all clean... except for some chlamydia." Anyway there's some itching and its kind of red and swollen (my vagina) and some discharge but i always have discharge so I don't know what to make of that. Anyway I was basically just wondering if it was a yeast infection or something more serious? And how I should treat a yeast infection? RIght now I lathered it in yogurt... haha I know that sounds weird but google advised me there anyway PLEASE HELP!