fearful for my new baby

I am currently pregnant with baby boy number 4 and I am so scared that there will be something wrong with him. My oldest is perfectly normal very shy but normal. Lil man after him had passed at 9 months old due to an angry and very jealous ex. An my now 2 yr lil boy is sick the doctors have no idea what is going on but he doesn't walk, crawl, can't hold his head up very well, and has to sit with support. I am currently 35 weeks pregnant with baby boy number for. And I'm so worried that something will be wrong ? Anyone else worried that something my be wrong with new baby.