My LMP says that I'm

Allyson • I'm 21 and pregnant with baby number 1. 💕
10 weeks 6 days and my doctor says that I'm 9 weeks 3 days. But I'm not sure cause I feel the way I should be at almost 11 weeks not 9 weeks. 
So my doctor changed my due days from January 12 to January 21. 
Is there any way my doctor could be wrong? 
I'm confused. 
Lol.