Last week I went in for an ultrsound and to hear a heart beat. I was suppose to be around 6 weeks pregnant. They told me my sac was only measuring at 4 weeks and they thought that they saw blood near the sac. I have had light cramping this whole pregnancy and lower back pain. I have no nausau and my breast don't hurt at all. I have gained less thn 5 pounds and the pregnancy test I took a few days ago said pregnant. Could I have had a misscariage?