When do I know I’m ovulating?

My boyfriend and I had sex while I was on my period but he pulled out way before he came so he didn’t finish in me. I know the chances of getting pregnant when your not ovulating or in your fertile window are literally zero. But what are the chances that I’m in my fertile window right now. Could I even get pregnant from his pre-cum ? I don’t know if what I’m saying is clear but I’m on my period, and had sex, and only pre cum is in my system. There’s no way I could get pregnant! I’m not paranoid but my boyfriends for some reason. I just want to show him yalls responses because he doesn’t believe me. Let me know what you guys think!!!! Is there a chance I could get pregnant. I think there’s zero chance but let me know what you all think