Blighted ovum and questions

Am

I'm 9 weeks tomorrow but two ultrasounds (one at 6.5 weeks and one at 7.5weeks) have shown no fetal pole. However, the ultrasounds do show a yolk sac and repeated blood tests showed my hcg (as of last saturday) was going up but not doubling. I'm wondering what other people's experiences were with the diagnosis process and how long it took?? I'm booked for a third ultrasound next week at 9.5 weeks. Any information on the whole process would be really appreciated!