Late period

So I know that unprotected sex can result in pregnancy. I know my actions have consequences. My question is who has actually gotten pregnant with the pull out method when it was done perfectly and has been done perfectly for years? My period is technically 10 days late estimated off my last period. About a week ago I started having pink discharge which usually meant my period was about to start. But all I got was alittle brown discharge and then now nothing but ewcm. I had unprotected sex. I cant remember dates but it was more than once over the course of November to December 15th and a few of those times we had been drinking, but we were never incoherent. If I am pregnant, I dont understand how it happened. He does it perfectly!