I am so sorry! Grief is indeed overwhelming for the person who is left behind.
I agree with the other replies. Do try to get some help for your son, but why not for you as well?
It will help you to vent some of this pain and a specialist will show you that it is ok to feel lonely and sad and totally lost but will also help you find ways to handle your feelings better. And there is one consolation which you will find to be totally true. TIME HEALS.
It took me a long time to accept the loss of my baby and a lot less the loss of my mother. But both were very- very painfull losses. But life still goes on and you WILL find the strength to feel better. I would n't think that actually getting on with your work is hurting you. Actually it does help by getting your mind off your loss even for brief periods of time.
God bless you!