Late period reasons?

So last time I had sex was April 22, 2017 and we used a condom. I got my period a couple of days after and also got my period in May and in June. It's currently July 18, 2017 and I'm 13 days late. I have been stressed about school and I've basically been PMSing this whole month since I still haven't gotten it. But just to be clear, there's no way I'm pregnant right?