Clarification

What if you have sex on the second to the last day of period 7/14 & have a completely normal period the next month 8/6. Do you think I could of got pregnant then ? Or more then likely the next month ? Found out I was pregnant 9/12 . From the first day of my last period 8/6 was a normal period . My dr said I conceived on 8/20 ish . So because my bby is measuring exactly on track from conceiving on the 20th of august but my friend told me you could be pregnant & have a period but I just wanted clarification that I’m not further along if my baby is measuring right on track , then that means 8/6 was a period .