Slow rising hcg with small gestational sac.

Hi have anyone done an ivf with slow rising hcg before? These are my hcg readings 12DP5ET 289 14DP5ET 449 16DP5ET 716 21DP5ET 1401 I had a ultrasound scan today (week 5 day 5) and doctor initially could not find my gestational sac but eventually found it but said it was smaller than expected. And was asked to monitor and come back again for the scan next week. Anyone have similar situations before? What are the chances for this to still be a viable pregnancy? #pleasehelp #ivfquestions #slowhcg #hcgnotdoubling