Gestational Sac but no yolk sac

I went to a private Ultrasound place just to do a Ultrasound since I can’t get into my dr office until like 7-8wks. The place I went used the abdomeninal ultrasound & she said it was saying I was 5wks & 1day so she said it was probably too early to see & said I could come in next week. I don’t understand though because I think I should be 6wks last time I had a blood test to check my hcg was on March 20 & my level was 3,336 & they said it coralated with my last period which would make me 6wks & pretty sure my hcg has doubled since then. I am honestly worried…… I am waiting for my drs nurse to call me back to see if maybe I can get in to get a transvaginal ultrasound. I am honestly worried idk what to think.