Advice?

Hailey • My name is Hailey, I`m 20 years old, And I have been with my soulmate for 2 Years and 3 months :)
Ever sense the day I started my period, It has always been spot on with the exact day it was going to start. It was very heathly and happend once a month for 4 days.
But for the past 6 months I have only had 2 period. And I'm 13 days late again, anyone know what might be causing this?