When I was depressed, these posts helped:
http://hyperboleandahalf.blogspot.com/2011/10/adventures-in-...
http://hyperboleandahalf.blogspot.com/2013/05/depression-par...
And if you like them, I find everything by her extremely funny, so go ahead and read up.
Good luck and hope you get better soon!
Try (1) SNRI or SSRI antidepressant (your doc will probably need to tweak your dose and try more than one drug), (2) exercise, even a little helps but if you were training for a marathon that would be ideal, (3) talk therapy, (4) spirituality, pets and other sources of meaning.
You should go at all of those with full force as depression can kill you just like cancer can.
If so, I'd start by finding a way to reclaim your emotions. You have the right to feel everything, positive and negative alike. To start with, here's an exercise. I want to you read my post and shout, "Hey, TheMoonToMyLeft, GO FUCK YOURSELF!". I want you to get angry, if you can. I want you to feel it, and act out that feeling.
If you can't even do that much, then you're in a deeper hole than you suspect and you need to call your local suicide prevention hotline ASAP.
Also, you need to start listening to heavy metal. Go fire up Paranoid, Master of Reality, and Sabbath Bloody Sabbath by Black Sabbath.