Heartbroken

I FINALLY got pregnant naturally.... after 6 years of trying, 6 rounds of iui, and 3 rounds of ivf (first failed, second got twins but lost one at 11 weeks, had our first girl, then got our second sweet girl) I never thought I could get pregnant naturally but it happened. The lines were SO strong. But our first ultrasound I was only measuring 6 weeks (I thought I was over 7) and heart rate was only 82. I hoped my dates were off, but I went in today and only measured 6+1 (a week later) and heart rate was 75. My heart is breaking. My husband is holding hope but my dr gave very little. This was our miracle... my heart is shattered and I still have to tell a very excited 3year old that the baby she has been loving on, may not be. 😢😩😭