Ultrasound at 5weeks no different then 4 :(

I went on Monday for an early ultrasound at 4weeks and 4days. I saw the gestational sack and egg yolk. It was super teeny though. None the less it was all there. He wanted me to come back three days later to see if we could see the fetal pole so exactly at 5weeks. And it didn't show anything different. I'm really worried :/ my levels were at 756 and I just had them redrawn today so I'll find out tomorrow if it doubling. But shouldn't I see something different? Even just the size? Help someone :(