Haven't gotten my period in 5 months?

I've never had sex, so I'm not pregnant, but I Haven't had my period for five months, so almost half a year. My periods usually come every 2 months and aren't very exact in the day, but five months has never happened before. I'm very worried. And recently all of a sudden I got really bad excruciating pelvic cramps that stayed for an hour-ish. I've never had those kind of cramps in my whole life. I have an appointment with a doctor to get revered to a gynecologist soon, but has anyone ever had anything similar? Got any ideas of what it could be? Do you think it's serious?