What does it mean when you 5 weeks pregnant but 3 weeks since you conceived ?

It means you...: Are counting correctly. The number of weeks pregnant is officially counted from the beginning of the last menstrual period prior to getting pregnant. The dating can be based on a 28-day menstrual cycle, especially if a woman has irregular periods or doesn't remember her last menstrual period. Thus, a woman is already "2 weeks pregnant" when she ovulates, and about "2 weeks + 1 day" at conception.