Could Pregnancy Symptoms With Absence Of Foetal Pole Be Due To Blighted Ovum?

I am pregnant my lmp was 12/19. I have very short periods that go between 29 and 31 days. I went in for an ultrasound 2/13, there was an sac but couldnt see the fetal pole or yolk sac and I was suppose to be 7 weeks and 6 days. my hcg levels were good according to the nurse. but i couldnt make it back this week. I still have pregnancy symptoms, what are my chances that it was too soone and the dates are wrong or is it a blighted ovum?