Thanks for writing in.
A small sac on ultrasound may indicate many things like a developing very early pregnancy, a missed miscarriage
or a blighted ovum
. Nothing can be said with the given details. Repeated scans 10-14 days apart or may be some hormone tests like serum beta hCG
may help in guiding us towards the fate of this pregnancy.
You should not be so worried just wait & see. Follow you doctor & hope every thing will turn out just fine this time.
Best of luck.