6 weeks can be too early to see via usual ultrasound, did they do a transvaginal one too? (otherwise known as dildocam)

I have twice now had blighted ovums, I get to 9 and a half weeks, have a scan but only yolk sac visible.
My hcg levels were still on target for where I should have been at (9 1/2 weeks) but gestational sac only measuring 4-5 wks. this is because (or so I was told) the placenta keeps producing the HCG even though the pregnancy isn't viable. my BT results coupled with the scan were the diagnosis for blighted ovum.

I also had no bleeding etc, the only sign for me that anything was wrong was a definite lack of morning sickness.

Good luck, I hope it was just too early for you to see yet. x