The count of weeks of the pregnancy time period called "gestational age" doesn't start on the day you got pregnant, it starts on the day your last period began. When the doc told you on November 19 that you were "6 weeks pregnant," he was saying 4 weeks since conception. I assume you know this, because you're talking about what you learned in November and evidently haven't been freaking out all the months from then to now. Is there some new problem or has someone said something that is making you nervous?
I know you already got an answer but I’m pretty sure you got pregnant AFTER your period, especially if it was a normal heavy period. Good luck with everything and congratulations on your baby