super worried...

So me and my boyfriend had sex for the first time about a week ago and we used a condom but we had sex twice and used the same one. He still took it off whenever he had to cum. My periods are irregular and I was about to get started on birth control this week. But as of now my period is 3 days late but could be normal but I am FREAKING out. I am not ready to have a kid and don't know what to do. Any advice??