Still no fetal pole/ yolk sac

Claudia
I'm so nervous and anxious. I have gone in for two vaginal ultrasounds and they haven't found the yolk sac. According to my last period they say I'm 6 weeks and 4 days. However the Dr says This could be cause I'm not as far along as we think. 
Anyone else any insight ? I do have a gestional sac and it's where it should be and it grew during the course of a week. 
Help ladies please??