Gestational sack no baby

At 9 weeks 2 days I got my first ultrasound and the gestational sack was there but no baby or yolk sack. I've had no cramps or bleeding all my levels are normal, but the sack was only measuring 6 weeks 6 days. I have an ob appointment tomorrow but it's just to do some blood work has anyone else ever had this happen. This is my 5th pregnancy and I've had two miscarriages already I just want to know one way or the other.