Lmp and ultrasound waaaay off

So my LMP was 7/31 and I am REGULAR!! Talking like clockwork! I was told my due date was 5/7/19. Which would put me at 10 weeks 3 days! Today I had some brownish pink bleeding going on and went to the ER only to have my first ultrasound to measure WAY SMALLER” I’m talking to small to even detect a heartbeat! My diagnosis was threatened miscarriage but they have no idea if my dates are off or if the baby stopped growing. Next Obgyn appointment isn’t for 2 WEEKS! Has this happened to anyone? I’m on pins and needles! First pregnancy since my miscarriage in April. I’m nervous 😟