pregnant? or what?

i’ve just started having sex (i’m 16) with my boyfriend and we always have used a condom. i’m now two weeks late on my period which was super worrying as i’m very regular. i took a $5 test and it was negative. i’m still not sure what’s happening as even when i’m stressed i get my period. does having sex for the first few times alter your period? should i be worried i’m pregnant? 😩😩