I believe what you experienced is "implantation bleeding". It happens 10-14 days after conception when the fertilized egg attaches itself to the uterine lining. Since ovulation occurs like a week before menstruation starts the implantation bleeding can be confused with a slightly late period, which makes it extra confusing to know if you're pregnant or not!

When I got pregnant I also had this little bit of bleeding when my period should have been. But since it was very light and my boobs got a lot more swollen/painful than usual I knew quickly something was off. But that was still 2-3 weeks after conception and not within days as this dunce seems to think is the norm.