Low hcg? 13 weeks? So confused please help

Heather • Wife💍, Mommy to: London 7/6/18🎀 Dakota, Due9/7💙

So I get my results sent to my phone before I see the doctor. So yes I will be seeing the doctor to discuss this but until then I'm trying to figure out what's going on?

This was my first hcg blood test I believe I was 5 or 6 weeks

Then I had all the Down syndrome tests and this hcg test last week at 13 weeks

I mean and that test was right after my ultrasound where I saw my baby who was measuring a few days ahead, had a strong heart beat, and was moving around. Like literally right after. So I don't get it! Why is it so low??