M.G.
Recognize his pain and of course allow him to show his emotions. However, whilst all this is going on try to distract him. I'd start with using PECS and/or social stories to allow him to redirect his thoughts and feelings.
Talk him through all the situations. For instance, when he stubbed his toe tell him something along the lines of "ouch, I know that hurts it hurts when I've done it too but it'll be okay." I know that may sound silly or whatnot but it's something I did/still do with my autistic son. I also did use PECS when my son was that age and completely nonverbal as well.
This advice however un/useful it is comes from a fellow mom of an autistic 7 year old boy who was nonverbal until June of 2013.
Hope you can work this out with your son. Best wishes.