being of service to others on a volunteer basis is a great way to find purpose. I am sure that your city has a plumbing program that requires classes for the students (my son is in one) can't you volunteer as a tutor? Lots of schools need volunteers as listeners, you just sit there and listen to the kids practice reading out loud. Or start a chess club. So many nursing homes and assisted living centers need someone to just talk to residents brighten there day--these are all things that are useful and if the depression comes can be stopped until you can fight your way back again.
hope this helps