Missed Period

PCOS runs in my family! I'll begin with that, I guess.

I'm 22 days late on my period, it just hasn't come. My sex drive isnt very high, and I'm pretty worried. As of this summer, my periods have varied in length and heaviness. Before it changed, it usually lasted 8 days with a light-medium flow. Now, its 6-7 days with incredibly light flow in the beginning and spotting towards the end. I'm scared that I have PCOS because I'm planning to have children when I'm older(I'm currently 15). It might be dur to stress because I just started sophomore year. So here's my question:

Is it normal to miss a period?