Worried!!!

I had an ultrasound done today and the baby is measuring that I am 4 weeks. According to my period I'm supposed to be 7 weeks. I had a miscarriage 2 months ago so I know that affected everything but I'm scared that I'm going to lose this baby as well. We did do blood work 2 weeks ago and my numbers were going up. I am having no cramping, brown blood but not enough to even wear a panty liner. I called my Dr to see what they are going to do. Waiting on their call is like waiting on pain to dry. I just want a healthy baby.