my last period was three months ago

I know I’m not pregnant because I’ve never had sex. I’m currently 20 years old, and I got my first period when I was 11. My period has always been irregular but In the past my doctor/ gynecologist would tell me it would eventually even out. Now that I’m almost 21 it worries me that I still go months without a period...I already made an appointment with my gynecologist. Does anyone else experience this or now what could be wrong. I know every person has a different reason as to why their body works a certain way, but I’m a bit lost at the moment.