What Causes Missed Periods And Pimple On Vagina?

Hi, I'm 15 years old and I'm a virgin. And I've been having some problems. I'm a softball player and I play softball half of the year. Towards the middle of my season I stopped having my period. And I haven't had it for a few months maybe around 5 or 6 months. And that worries me. Sometimes I get these really bad stomach pains. And then I found then pimple looking thing on my vagina and I don't know what it is. Is that a normal thing to get on your vagina?