Late periods

Shawna • Just a normal girl tracking her period
So I'm 16 and over my past three cycles, my cycles have been getting steadily longer. 
It went from 36, 39, 46, and now I'm on day 52 of my current one. My period is 16 days late.
Should I be worried and should I purchase a pregnancy test?
I'm scared that I'm not ovulating correctly, or that I may be pregnant.