Am I 3 weeks or 4 weeks?

Jennifer • I had my rainbow bay 4/22/19 and have been ttc sense, had a miscarriage 10/22 and now pregnant again hoping this will be my second rainbow baby🙏🏽

Every time I put in my period online or the 3 days in which I conceived it says I’m 4 weeks but my doctor did a blood test and the nurse said I’m about 3 weeks! Can someone explain? My period was September 14-19 and we had sex the 26-29th which was was the week I was schedule to ovulate. I’m confused someone help please!