Date confusion

Jen
I'm confused by dates! My doc said my due date was March 20th but I'm confused on how far along I am because he changed my due date twice! Anyone else due March 20th that can tell me how far along you are?  My ultrasound last week dated the baby at 8w 6d so now I'm lost! He said baby is right on track but I don't feel like I am! Lol Thanks!