Cramping

So yesterday I went to the hospital for some sharp pains in my lower right abdomen. After a 6 hour wait, I was informed that my baby is measuring 6weeks 0days. We were able to see our little love bug with a transvaginal ultrasound, the baby is in my uterus, which means it isn't a ectopic pregnancy... right? The yolk stim wasn't formed yet, and they didn't detect a heartbeat, he talked to my OB and we have to have another ultrasound later this week and have more tests done.. what does this mean? I've miscarried in the past and I am very scared of it happening again.