Losing virginity

Hi! Can you get pregnant when you're at your 4th day of period? When we were having sex, we kind of discussing that it's okay to cum inside me since Im on my 4th day of period. But, we were both doubtful. Then as sex goes. He pulls out and as if his thing got tired. I asked him if we cummed inside me and he said he wasn't sure. Then I asked him again after we ate, and he said he didn't. Because he'll know if he cummed.

Do you gals ever had experience if the guy knew or not he cummed?