threatened miscarriage

Hello,

I would be 7 +3 today.  I started bleeding last Friday, started with brown spotting and went onto what I would describe as a heavy period.  I have had no pain.  I went to the hospital and had a scan at the early pregnancy unit last Monday.  I would have been 6+4.  All they could see was a fluid sac from the scan. no embryo etc.  
I have to go back on Wednesday for another scan.  

The nurse I seen advised that unless my dates are wrong it looked doubtful

My bleeding has just about stopped, as it is more like spotting now, however i still have a positive pregnancy test.  i dont know if this is just my hormone levels.  the waiting is really playing mind games with me 

Has anyone else experienced anything like this.

From the start of the pregnancy I have had no symptons, however this was the same in my first pregnancy?