Losing a child is about as bad as it gets. When it's your only child, it's difficult to imagine for someone who hasn't been there.
If it's possible, get involved in something productive that will occupy your time and allow you to be around other people. The more time you spend alone and the more you think about it, the harder the task of recovery will become. You can't change what's happened but you can still make a difference in the world. You have to force yourself to try.
Good Luck.