Help!!

I had unprotected sex 5 days ago and my period is due today but it’s not here. My period cycles are sort of irregular, about 35-40 days. I already know I should start taking birth control, i’m looking into that now. but is it even possible to get pregnant that close to my period? I’m not sure if i’m late because i’ve been stressing or because i might be pregnant. he did NOT cum in me, but i’m worried about precum.