Pregnant?

I had unprotected sex thursday the 10th and he came on my stomach not inside me. We did nothing for two weeks until yesterday monday the 21st he came inside me. My period was supposed to start sunday but it didn't start and usually i'm 2-3 days late sometimes 4. We had sex anyways because i still wasn't bleeding and he came inside me but i went to the bathroom an hour later and saw two blood drops and thought i was starting my period so i woke up this morning and got my period. Is it even possible to get pregnant if at the start of your period? i'm not trying but i'm also not, not trying. any comments appreciated!!