The 1-3 weeks was from the doctor. I asked if she meant from ovulation and she said 'no 1-3 weeks pregnant'. It was at that point that i realised she was the biggest idiot ever, especially since I got my BFP several days before the blood test.
She was reading it from the pathology report. It says 'gestational age' and then the different ages and the range of HCG levels.
I'm going to book in for my dating scan in three weeks time. I'll find out then if all is well or not (I'll be 7-8 weeks along I guess, so there should be a heartbeat). Until then, I've managed to convince myself that everything is ok, although I'm still worried about the lack of morning sickness.