BH - I know it is frustrating but try to not let it get to. You may never know the reasons why and you need to accept it. There are many things that happen in this world every day to good people and they never know why. You and I should be no different. I have a very close friend of mine who lost her child at the age of 24 to cancer. She has to live with it every day and still has no answer as to why. Be thankful for all that you have, be thankful for your healthy children and that you got to experience them grow up in household with their mom and dad under one roof. Something that my kids will never get to experience.
Try to not get bogged down in the details. You have a lot to be thankful for so try to focus on that.