Bleeding and un known of weeks during pregnancy

hey.  is my second pregnancy- 1st pregnancy was lost to a miscarriage at 12+5 weeks pregnant. 

6 month later I am pregnant again,  for the past 2 days I have had bleeding. First day - brownie red discharge / Blood (tmi) pains in back & side. this went on for about an hour 

second day the same more of just red today and has been on and off, more when I wipe (atmI) i have had in internal and outernal  at hospital today who said I look 5 1/2 weeks. 

I had a private scan before bleeding 1 week ago who said I looked roughly 6 weeks pregnant.

From calculations I should be about 8 weeks pregnant. so I'm pretty confused and extremely worried. has this happened to anyone before?