I'm sorry but I can't say I understand depression, that's not to say that I don't believe it exsists, and I sympathise with anyone who suffers from it.  If it gave you such a lift when you were helping people streety, why not try to occupy some of your spare time doing just that.  You could volunteer to work in a charity shop or, do you have befriending schemes near you?  My daughter used to volunteer at a drop in centre for adults with learning disabilities.  They do art work or cooking so you don't need any special training to help them bake cup cakes or make veg soup etc. try here (if it works) I think it'll tell you more about it.  www.thebefriendingscheme.org.uk/‎  Hope you feel better soon.xx.