Hello I Had My Period In Early To Middle Of

Hello I had my period in early to middle of agust I had sex close to the end of August to the middle of it I got my period in September on the 7th I found out I was pregnant October 9th I did a conception calculator to chart possible time of conception which was around September 21st I wanted to know could I have conceived in September ? And not August because I got my period in September ? If I where to conceive in August I would of missed my period in September i believe ? Please help