What Causes Pimple On Lip Of Vagina After Having Protected Sex?

i am 18, i recently had protected sex with my boyfriend but now i have a pimple on the lip of my vagina and i think bumps that itch on the side of my vagina opening. sort of burns a bit when i pee too! i've never had sex with anyone else. and he hasnt either. and this has never happened before. do i have herpes?!