Ive missed 2 periods and im a virgin, whats going on?

ive had 2 missed periods the last time i had it was april. i ended april 1st and started again 2 weeks later(not sure why) and ended a week after. i haven't had my period since then and im a virgin and cant be pregnant. i have masturbated before, only by straddling a pillow and going back and forth. can someone PLEASE PLEASE help me.