When was my baby conceived?

LMP was Jan. 8 Had on Jan 17.'09 During he didn't inside. Jan 26 he did d inside.My first doctor visit was Feb 21st. He calculated from day of LMP He said i was 6wks pregnant. Few days ago March 11th I Had a sonogram and shows I'm now only little over 6wks. When was baby conceived. Jan 18 0r Jan 26th?