Help me

Yesterday I went to the doc to get my regular check up and since I missed my ultrasound appt. my doc decided to see if she can hear the heartbeat on her own, nothing. I went inside another room to do an ultrasound and she claimed she couldn't see anything. Based on my last menstrual I should be 11 wks so how can you not see anything? I went for an emergency ultrasound for them to only tell me that the don't see a baby the see an abnormal sac but no baby. Now I'm confused. I asked if I had a miscarriage they said no I'm probably just a couple of weeks prego which is IMPOSSIBLE. Now they want me to do blood work to see my hormonal level then come back for another ultrasound. I'm unsure what is going on can someone plz give me some insight.