I have struggled with depressive disorder for my whole life. I've tried at least 15 different medications and either they didn't work or the side effects were worse than the disease. Been through therapy and that helps sometimes. I recently went through a study at UCLA and did electro magnetic therapy which worked for a while, but now am back to the struggle although my symptoms have lessened.
I have found a group called recovery international, it is helping because it is theory that works by retraining you thought process, with the added benefit of being able to go to a group sort of like AA. In my experience depression is an illness, that for me , is going to be life long, how depressing is that
You can get the reading materials online, just google recovery international.
Isolation is part of the disease and I know it's hard to be social when you really don't want to be. I have to force myself quite often to do things, but usually enjoy myself when I do. My best advice is make a program that works for you. For me it is exercise, duh :-), keeping my mind busy with positive thoughts, and doing things that bring me joy. And remember you are not alone.