Anyone here ever gotten pregnant during infertile window?

My bf and I had unprotected sex and he ejaculated inside me. My period is due in 6 days so I'm on my second infertile window of this cycle. Was just wondering if anyone has gotten pregnant from a similar situation. I know the "risk" and fertility rating are extremely low but we aren't financially ready for a child and not sure if Plan B would be neccesary here. Thanks for any responses in advance!