I miscarried at 6 weeks almost 5 weeks ago.

They scanned me when I lost the baby and said that I had passed everything. I did a pregnancy test on Sunday and it was a strong positive. I have had a scan today and they have said they can see fluid and are unsure if this is a new pregnancy or an old one. My HCG levels are currently 168. Has this happened to anybody else? What was the outcome?