Oh my goodness, I am so very sorry for what you and your family are going through. Please know you are in my thoughts and prayers. Forgive me for saying this if it upsets you but that driver needs to be given the stiffest penalty possible and should never see the light of day again if he/she wasn't having some sort of medical episode.
One thing that may help you get through this time a little easier, although nothing will really make this time easy on you, is going to see a counselor at your local Hospice office. The service is free to anyone who has lost a loved one. I highly recommend their services. They were a HUGE help to me when I lost someone suddenly and unexpectedly.
Remember to take it one day at a time. Don't look way out into the future because right now you have to focus on yourself getting through each day, each minute. Remember to take time to take care of yourself and take time to be alone if that is what you need. It is okay for you to take time to do something good for yourself too. There is nothing wrong with that. If you want to go get a manicure or pedicure that is okay, you are not being selfish. You need time for that. Honestly you do because if you don't you will get run down and possibly sick. Take care of yourself for your son as well as for yourself. And remember you don't have to take care of everyone around you right now, let them take care of you. I hope this come across as trying to be helpful because that's why I'm trying to do.