Help, am I pregnant!?

Hey girls, I've been stressing out with whether I'm pregos or not.

Today, I'm 19 DAYS late on my period and the previous periods were always right on time.

So I finally brought myself to go get a pregnancy test, waited 5 minutes and it comes out negative.

What im wondering is why is my period so late and could the rest be wrong?

Also, I live with my boyfriend and we have quite a bit of unprotected sex