Doc driving me crazy... Not sure what's next

So I had an app I time to today. Husband came a long for the first time. Doc was running late so he ended up having to leave me :/ of course he leaves and try call me in. Tech is doing the sonogram, says my baby is 5 w 6 d. I ask her to repeat that she hedges a little prints my pictures and says 5w 6 days.  They take me to go see my doc. She breezes in telling me everything looks great and am like "OH REALLY?! Because I feel like ice been measuring 5 weeks for two weeks?" So she pulls all my sonograms and realized I was right- I was 5'w2 on my first scan 5w6 second scan and now on my third baby grew. It still measured 5w 6. So now she basically makes the sad face and says oh you may not make it lets get some blood work and I'll see you again Tuesday for a new scan. I have had no bleeding  o cramps. My blood work came back Hcg is 19000+ progesterone is 25.4 and my tsh is 1.66. All these numbers sound good so why is my baby not growing fast enough. I'm afraid of having a third miscarriage In Less than a year and literally right after my second one. In trying to be positive but it's so hard. Anyone know anything about slow growing fetuses/babies?