mixed emotions after the loss of a child

Marcie
I'm 41 (almost 42) 
I just found out I'm pregnant and having really mixed emotions as on May 9th my 20 year old son died in his sleep from unknown causes. 
Why would god take my child and then give me another? 
  I'm struggling to be happy,  tho we tried to get pregnant up until a few months ago and decided to stop trying. I had a miscarriage in Nov at 8 weeks 
My period was may 30th -4th and we only had sex on the 10th  because I had my gallbladder removed before that   
I have 3 daughters ages 23, 16 and 2
My son would have been 21 in 3 days 
I want to feel happy but....  I'm still mourning my son and terrified of another miscarriage.  My hands literally shake I don't know what to do with myself.