rainbow baby and terrified

Hi all! 
I'm 19+3 weeks with my rainbow baby.  My first baby came at 32 weeks and only lived for an hour after birth. 
Now, this pregnancy I'm terrified with every little thing.  For example, last week I had damp underwear - it was sweat.  Last today and this morning, I had some cramping and lower back aches.  My doctor told me that these types of aches are completely normal. But I'm terrified. 
I'm just so anxious that something is going to go wrong and my heart can't take any more pain. 
Anyone else going though this? How are you coping?!