HCG not doubling but heard heartbeat

keep

1 beta 21 NoV (15 dpo) : 215

2 beta 24 nov (18 dpo ) : 837

3 beta 26 nov (21 dpo ) : 1469

4 beta 28 nov (24 dpo ) : 2033

5 beta 30 nov (26 dpo ) : 2433

6 beta 5 dec ( 31 dpo ) :4301

7 beta 9 dec (36 dpo ) : 5600

My progesterone level was 8 on 30 nov my doctor put me on progesteron pills my progesterone went from 8 to 28 on dec 5 . Dec 9 it was again 6 . I have no idea why it got so low ?

I went for ultrasound at 5 week 6 day to rule out ectopic . They saw g sac there and it was measuring as 4 week 6 days .I went again for ultrasound at 7 week they saw sac through abdominal ultrasound but when they did vaginal ultrasound they saw baby with heart beat 116 but baby was measuring only 5 week 6 days . Please can you help me to understand whats happening ? Do you think everything will be workout at the end ?