HcG levels slowly decreasing

ashs1406

So this is my first pregancy. On 07/19 i took a HPT it came back positive. The nexy day on 07/20 I got a hcg blood test and my levels were at 31,813 confirming we were def pregnant. I had a sono done on 07/25 with bloodwork heartbeat was not found yet and my hcg levels dropped to 30,679. The doctor told me to prepare for a miscarriage he told me to get my levels checked again in 2 days with another sono to see a little more. My levels on 07/27 was 30,236.1 and when i got my sono done that day the tech had a newer machine and could see two yolk sacs instead of one from what we could tell. The doctor was trying to get me to have a d/c this coming thursday 08/02. I also had my levels checked again today and they were at 25,466. I have had no symptoms of miscarrying, no pain or bleeding I still feel like I have since i found out i was pregnant. still feels some pulls a tiny little pinches with very mild cramping. Is it possible i could have a vanishing twin and still have one that is viable? I don't have regular periods either so I don't know exactly when we conceived.