Can you get pregnant on your period?

Okay this is probably a dumb question and I'm pretty sure I already know the answer but, I had sex with my husband on what was supposed to be the 5th day of my period. I say supposed to be because it stopped after we had sex. So we had sex and he came in me because he thought I couldn't get pregnant on my period. I've felt off ever since & my discharge is different. If I did get pregnant when can I test?