Hello Ali, my condolences on your loss.
I have to agree with everything Julie says.
You'll get through the initial stages one way or another, horrible gut-wrenching times I know but we find the strength from somewhere and eventually you'll find that you have the odd day here and there that isn't so bad.
I hope that you get good support at work, if possible I would suggest a private chat with your line manager before you start back perhaps to arrange a phased return. I think it's important not to plunge in at the deep end and get overwhelmed.
It's a bewildering time, at least it was for me, when you experience feelings,thoughts and emotions that take you by surprise. If you can, talk things over from time to time with your son and let him know how you're feeling. Explain to him that nothing he can say or do will make things better but at least you still have one another. All too often this is a time when there are fallings out and that should never happen for the want of a bit of honesty. Oh no - am I preaching - if so forgive me, it's well meant