Is it possible to conceive a week before AF is supposed to show up??

I know ovulation could occur a little late which is what I think happened to me. I usually never have any cramping days before AF is supposed to show up but my husband and I had unprotected sex and he ejaculated inside me which we thought was fine because we thought no way you could get pregnant just a week before AF is due but after that I got small light cramps that would come and go which I thought was weird and just a day before AF was supposed to show up I had brown like fish charge and I ended up having a what I thought was a weird “period” unusual from what my period usually is and I was wondering what was going on...but has anyone experienced anything like this?? And was actually pregnant?? I had read that some woman had a “period” before they found out they were actually pregnant. Thoughts?? 🤔