I Started Microgestin 1.5/30 On June 20th, The Last Time

I started Microgestin 1.5/30 on June 20th, the last time I got my period. I have had sex with my boyfriend starting in early June, we used condoms every time, however there was one time when he thought the condom slipped off but he checked it and said it was fine. It’s now July 28th and I haven’t had my period, could I be pregnant?