is this normal?!

Danielle • I have a 6 year old son and am pregnant with baby number 3! I had a miscarriage and am now 36 weeks!
I took a pregnancy test last week and it came up positive. Tonight I was having stomach pains so I went to the ER and had a transvaginal ultrasound and they saw a sac but no fetus yet. Is it too early? It measured 5 1/2 weeks and my HCG is at 15,000. Just went through a miscarriage two months ago so I'm praying this isn't the case.