Could I be pregnant?

A couple days ago my boyfriend and I had sex. He had a condom on but, after he finished, when he pulled out the condom was inside me. We don't think this happened until he pulled out and are pretty sure that everything was inside the condom but I am worried. I downloaded this app after it happened because I was so worried, before this I loosely tracked my cycle on my own. I don't think I'll start my period until later this week or early next week but I don't know what that means as far as fertility and my chances of becoming pregnant.