Suprise of the day I'm having twins.

I had a 3d ultrasound approx at 5 weeks and it showed two sac but one apparently is smaller than the other which the doc is concerned about. And also my prostegerone levels are apparently low to which had been taken on cd 28 before I even knew I was preg it was 22.5 which Doc said is low to carry the baby so she prescribed me duphaston and told me to come in after 10 days, anyone in the same boat or have some knowledge in this?? Xx