6 & 1/2 weeks empty gestation sac

[Bublara]

Hi,  I went for a u/s at 6 and half weeks (since lmp) and gestation sac was empty... Measured between week 4 and week 5.

My hcg levels also measure between week 4&5, but I should be at least 6&1/2 weeks now...

I have to wait 10 days for a follow up ultrasound which is extremely stressful.. I am not experiencing any strong pregnancy symptoms either, very worried!