Empty sac at 11+3 weeks but still showing positive on a pregnancy test?

can anyone tell me if they have gone for their dating scan only to find the sac is empty please? I had my scan today and the sonographer couldn't find anything. I know I haven't physically miscarried because this would be my second (my first m/c was at 7 weeks) so I know what it feels like. I'm just so confused and am currently waiting on another scan appointment to confirm the findings. many thanks.