I had the same thing hun but mine was at 6w2d and they saw nothing, just a thickened lining. Told me was either too early, miscarriage or ectopic. Had 3 lots of hcg and unfortunately it was rising but doubling. A 2nd scan a week later showed a small sac but sadly after 3 more scans nothing has ever developed in it.
My epau will not scan before 6 weeks as they say scans are always inconclusive this early. I think if you're hcg is doubling then its prob just too early. I got all my blood results back the same day and one of them was even on xmas day and the on call Dr rung me. You can always ring and ask for them if they don't ring you.
A lot of ladies on here have had early scans which have not gone well but then had baby show up on later ones so don't give up hope yet, its still really early.
Keep us posted, everything crossed for you xxx