Two periods in one month?

I've had my period since I was 12 years old and it's NEVER been regular. I'm almost 18 now. I get severe cramping and the longest I've gone without is 8 months. The shortest being one week. I'm still a virgin so it has nothing to do with any of that, but geez, does anyone know what the cause of this stuff is? BEFORE I turn to the stupid gynecologist? I brought up PCOS, because I have other symptoms, but oy, is this ever going to go away? These cramps are making me feel like I'm dying. :(