I have also had a blighted ovum, which wasn't picked up until 13 weeks, when I started heavily bleeding and big chunks of hard blood came out of me

But I have also had super early scans with following pregnancies, and have had the same thing happen, couldn't see a fetal pole, but there was a sac. So I'm sure its all good, as your HCG is increasing and you have strong symptoms, so don't stress, good luck for tomorrow