How far along am I?

Today, I had my third ultrasound. According to my first two ultrasounds I should be about 13 weeks and 1 day. These ultrasounds also matched up with the date of my last period. Today, my ultrasound measured the baby at 14 weeks and 2 days! I was always told ultrasounds are pretty accurate so I was surprised to see that this one showed me farther along than the first two. .i also wonder if maybe I'm just going to have a big baby? I wasn't sure if it was possible to tell at this point. .or has anyone else had that happen?