sorry forgot to add ive only recently found out im pg so can only be around 4 - 5 weeks. the reason for me having blood taken so early is because ive had an ectopic pg before so they want to make sure its not happening again.
I had this with 1st pregnancy. Don't remember the exact results, but levels were on the very low side of normal though not doubling in 48 hours. I was referred for a scan, which showed a heartbeat, but the sac was smaller than it should have been. I miscarried a few days after that at 7+1.
Fingers crossed for a better outcome for you, the not doubling thing isn't always a bad sign. I reckon there will be more stories of positive outcomes.