LATE period


So I have always have a very normal period. I’ve never been more that 2 days late. I was supposed to start 2 weeks ago, and when I didn’t I got very worried. I took a pregnancy test and it came back negative. I figured it was just too early to tell so I decided I would wait a couple weeks and take another one. BUT I just started my period. Why was it so late???? I’m only 18 so I feel like that’s a little strange... has this ever happened to you guys? Do you know why this would happen?