Twins??

So two years ago I had a blighted ovum at 8 weeks and was told during big ultrasound to confirm BO, uterus was tilted. Fast forward to now. Lmp was oct 26. Had first positive test Nov 24. First ultrasound Dec 10, sac measured 4 weeks. 8 days later had another ultrasound that revealed 2 sacs! The same sac from before measured 5 weeks and the other sac is measuring smaller. Qhcg levels were in the 8 thousands. My doctor isn't exactly sure what is going on. We talked about the possibility of "vanishing twin", ovulating twice and ect. Just wondering if this has happened to anyone else? I have another ultrasound on Tuesday, which will be 4 days after my last one. Not sure if there will be any difference. Also, yolk sac was not able to be seen yet. Could that be because of my tilted uterus?