I am said to be 7 weeks pregnant but on a oregnancy calendar I am said to be 9 weeks. Do I go by the first day of my last period or do I do from 2 weeks after? Just want to know so I so I can see what my body is doing in the right week and what to tell people

Said by who to be 7 weeks?

Due dates are guesses and estimates based on your est dates you had sex after your last period. Two weeks after is often used as a crude estimate unless you know specific dates you had sex durin that several week period.

After that, the doctors also use estimated dates based on size of the fetus.

So you use the estimate that the doctor gives you, knowing of course it is merely an educated guess