I'm confused....

Michaela
My periods have always been as regular as clockwork, 28 days. I've been late 4 times, 1 healthy pregnancy, 2 CP, and now. According to my calculations, (and glow) I'm 6 weeks 5 days, but when I went for an ultrasound yesterday, the size was more like 4wks 3 days. It was similar with my son. Anyone else have this,