Low hcg levels during pregnancy?

Short back story just to understand what's going on:

I got pregnant in October of 2017. My baby was diagnosed with bilateral CDH at 22 weeks I carried to term and gave birth July 7th 2018 he passed away an hour after he was born. Shortly after losing him I discovered I was pregnant again. I got pregnant at the end of September 2018. I went to appointments weekly because I was considered high risk. At 10 weeks I got a blood test done to check my HCG levels and to check if the baby had anything wrong with it. The results came back inconclusive I had my first ultrasound at 11 weeks everything looked great! We had a dancing baby that had a strong heart beat and was normal size for gestational age. At 13 weeks my doctor sent me to get the same blood test again because he thought maybe I was to early the first time. The same appointment I got to hear my babys heart beat again it was strong and steady.

Im now 14 weeks 1 day and my doctor called me around 5:00 pm and said my results came back inconclusive again. He said my HCG levels never went up. Before explaining what this meant he tried to ensure me that it's not 100% he said some womens results just dont adjust properly but in my case he strongly believes there is something wrong with the baby. He didnt go into very much detail of what the problem could be, he wants to send me to a specialist and he wants me to get an amniocentesis. My heart dropped to my stomach as he explained that if my baby is sick it will more then likely lead to miscarriage if I get the amnio done. He said i dont have to get it done and i can wait until I'm 18 weeks and they will have me go in for an ultrasound and they will be able to see more. He kept telling me not to get worked up but how could i not? I just lost my son and now i could be losing my rainbow baby. My heart is aching and I'm honestly feeling so defeated right now. Is there any hope? Has anyone else experienced this and had a healthy baby? Should I get the amniocentesis done? I know it's up to me but I dont want to do this. I just want my baby to be okay. I know one thing for sure when I go see the specialist I'm going to request that they give me an ultrasound that day. I've gone to this doctor with my son and I know she will try and do everything she can for me. I just wish this never had to happen to anyone. It's the worst pain a woman can feel. Any advice will help. Thanks in advance.