My doctor said im 14weeks but based on my last period and when i had sex i should be 13weeks so did the baby grow fast? or????

Date estimates: In the world of pregnancy date estimates, all dates are estimates for a natural pregnancy. That means 14 weeks is an estimate, usually plus or minus 1 week. Thus, 14 weeks is the same thing as 13 weeks. Likewise, 14 weeks is the same thing as 15 weeks. Only in an artificial in-vitro fertilization pregnancy is it possible to know the exact conception date.