I need help

So I had unprotected sex with my ex bf(we were together at that time)  and the very next day I got my period. And this month I was supposed to get it on the 19th and I was 2 days late but I got my period. And today I was noticing that my nipples are a bit darker could that be a sign I could of pregnancy or am I pregnant? I'm very scared i don't want to be pregnant I'm in college and not ready for a baby, please help me out girls I am freaking out.