Different conception question?

Maybe I should rephrase the question. Like I said I am 31 weeks pregnant and I was reading a question on here a girl posted about when do we think she conceived. And answer she had received stated that if the dr told her she was 6 weeks pregnant, that really means she is 8 weeks pregnant. I know they go by the date of your last period but say the first day of my last period was the first week of april. That is 7 weeks ago. The dr would tell me that Im 7 weeks pregnant but would that mean (according to that answer I read) that Im really 9 weeks pregnant? When they calculate it, does it mean you got pregnant before your last period or after your last period? Im just curious. Thanks for your answers!!!