How hard this must be for you. I am so sorry for the loss of your first child. I had similar feelings after my first grandson was born. A dear friend of mine had a grandson born just a few weeks after mine. They both had the same first and middle names. Her grandson passed away from RSV at about 6 weeks of age. It was so stressful to me. I would sit and watch my grandson breathe while he was sleeping and I was not able to sleep at all.
As my daughter had more children I would catch myself being distant from them and thinking things like they might die and I didn't want to get too close to them so it wouldn't hurt so much. I had lots of leftover issues about this friends grand-baby passing away. I had a hard time opening up and getting attached to the rest of them until they were several months old.
My sister had a stillborn baby her first pregnancy. The baby was not very active then just stopped moving. She was 8 1/2 months along. I think being very non active is a sign, not too much activity.
I think if you talk to your doc about your fears he might be able to do something to help. Is there some type of monitor that you can wear? That will keep track of the baby's heart beat?
Perhaps playing some CD's that are uplifting and calming might help too. I find that when I am stressing out if I put some Peaceful Ocean Surf in the player or something soft and quiet I can drift off to sleep much quicker than without anything. During the day I often turn on local religious music. It doesn't have bad language, questionable topics for the daily trivia questions, rude comments about this politician or that business. It's pretty much enjoyable, since we have 3-4 of them I can always find one playing good music, I don't listen to the preaching on it. I do like some of the programs though like Money Matters.