Hi, I had unprotective sex ONCE with my boyfriend and now my period is a week late...
I had sex a week before my period was supposed to arrive. Is it likely I'm pregnant?

Take the test! It doesn't hurt.

Likely is not the right word, possible is the word. Of course even with protection it is possible, since no protection is 100 percent. So I am not sure if you were also having protected sex.

But for some couples they may have sex for months before they get pregnant. For other couples they will get pregnant the first time they have sex.

But of course things like infections or STD or stress, or hormone issues can make you late or even miss your period.

You may want to wait perhaps another week and if still no period, try a Home pregnancy test.