Large sac but no pole or yolk sac :(

[SophiaAlex]

Hi I am 5 weeks+1 today. I went for a scan under the drs request (recurrent misscarriages) and there's still no yolk sac but the sac is measuring 7.8mm, l've read online by the time your sac is measuring this big you should at least see a yolk sac, I got my 3+ on the clearblue digital on Saturday (31st) meaning my levels should be at least 2,700- I know these aren't always 100% accurate however they've never really been wrong for me and again at 2,100 there should be at least a yolk sac. I'm so incredibly worried as I'm really nearly 6 weeks (going off my last period) it's only because I'm a late ovulater (day 20) that I am earlier than what I'd be with my period dates.
Has anyone else had this? My concern is that everything online says I should have a yolk sac with a gestational sac of nearly 8mm and if there isn't one it's a sign of a blighted ovum
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I had a scan at 5+1 weeks and there was barely anything to see at all. They couldn't even hazard a guess if it would be a viable pregnancy or not (I was there due to a massive bleed). My levels were 14500 though, which was alarmingly high (I think perhaps it might have been a multiple pregnancy and the huge bleed was part of that).

@CandiedPrincess thank you, what I'm most concerned about is how big the sac is. Everything I've read online you should at least see a yolk sac in a 7-8mm gestation sac :(