What Causes Delayed Period After Having Protected Sex?

hi

I was supposed to get my periods on 12Feb and I havnt got them till today that is 26th Feb..is this delay ok..I did a pregnancy test 4 days back..I hav always had sex with protection..d last time I had sex was 14 Feb.

I am almost 18.

what should I.do?!

pls help

I have always had delayed periods.

but this time the delay is too much and.its scaring me.