hcg question for twin mamas

So I know hcg can't actually predict if you are having twins or not but this is my second pregnancy with Clomid / trigger shot / <a href="https://glowing.com/glow-fertility-program">IUI</a> and my hcg levels were sooo much lower with my son. I got a dark positive test 2 days before my missed period (first time I tested). My hcg at 16 dpo was 606, at 19 dpo was 2,653 and at 23 dpo (today) 12,313. They did an ultrasound today and there is only one sac measuring a few days ahead at 5 weeks 5 days (I'm 5w 2d) and what she thought was just one yolk but she couldn't be sure. I get another ultrasound in a week. Should I expect there to be 2? Just curious as to what your thoughts are.