Hi there. Actually this DOES happen. I had a period of about a year and a half in which my period came every three to four months only because of a hormonal imbalance (produced too much estrogen, not serious). It resolved on its own.
I would say that if you have never spoken to your doctor about this, it is time to do so. But don't be overly worried. It is not at all uncommon for someone your age to be irregular even when they hadn't been previously.
good luck
You should see a doctor as soon as possible. If you are not sexually active missing your period could be a sign of something serious. Don't ignore it.
This could also be due to stress. I would talk to a female role model in your life, mom, aunt etc. and see what they think about it being normal vs Dr.