Determining how many weeks before going to the dr.

Silver

Everywhere I read says to use the FIRST day of your LAST period and count from there to see how many weeks.

A friend of mine told me I should be counting from the day of conception...

Which is correct!?

My last period was May 18-22

I took an ovulation test June 2nd and it was positive. I also had sex that night so I'm assuming that is about the time of conception.....

I probably sound like an idiot.. I'm just new to it all...