Confirm twins next appt?

I found out I was pregnant 3 weeks ago I had a ultrasound last week but it wasn't enough to date,.. I went back today and my doc said it might be twins but we won't know for sure for another 2 weeks😱😱😱😱. I was extremely relieved to see the heart flicker,.. Twins run on both sides,.. And I honestly thought I was way farther along than barely 6 weeks. The dr thought I was 9   So my questions is.  Can the yolk move??   From my two different sonograms I see them in a different spot?   Could it be that one is hiding ?    The brighter one is the newer one,..  On the first the yolk is on the right and the second one. THO hard to see is on the left?