So my boyfriend and I had sex a day after my period ended which is a couple days before I start ovulating. We used a condom but I know that they’re not always effective and sperm lives in the vagina for up to 3-5 day. Should I be worried? My period is supposed to start today and I’m trying not to be stressed. Please help, I’m only 16

Update: I was supposed to get my period yesterday but I haven’t yet, but yesterday I had really bad cramps and my lower back hurt, what does this mean?