I am sixteen years old. i started my period when i was nine. but for the past three or so years my period has been very irregular. it'll skip for, at the most, 2 1/2 months. My mom's not sure what's going on. i have no older sister to ask for help. I dont know what to do! I've never had sex, so i know it's not some sort of STD. Could someone please help me?