Horrible feeling can't shake it

I am pregnant with my second child (15 weeks) and ever since I conceived I feel like this baby isn't going to last . I hate feeling this way. I never felt this way when I was pregnant with my son . But again I didn't have this app. And I read story after story of women losing their baby and o am heart broken for them. I guess I feel like I can't be blessed with two beautiful children. I don't know why I feel this way. I hate it ! I'm also not excited at all this time around in way sicker and so tired and again I feel bad I'm not excited  . Don't get me wrong I know I love this baby but I can't help but feel this way . Is it normal ? Be honest but nice please !