To all expecting mothers ?? I'm at 17 weeks and 5 days according to my…

To all expecting mothers ?? I'm at 17 weeks and 5 days according to my doctor. My last period was September 17th - 21st, 2022. My last period ended on September 26th and I had spotting until October 5th. The apps show conception when I still had my period ? How can I get a more accurate calculation? It’s unclear what my actual due date is. Every ultrasound technician and gynecologist gives me different dates, although my doctor says that the obstetric term is about two weeks ahead.