The most insidious thing about depression is the fact that it destroys your motivation and enthusiasm, which in turn prevents you, in a way, of doing the things that lift your spirits. It compromises your coping mechanism, and so everything seems hopeless. You think of your future, and that thing called 'happiness' seems like an alien concept. It's a bitch of a situation to be in, isn't it? I know when I was at my lowest, the world appeared to have lost all colour. It reminds me a lot of that song 'End of the World' by Skeeter Davis.
I don't really know your story, so forgive me if I'm asking an obvious question, but have you tried talking to a psychologist? I, personally, dislike that kind of talking-therapy as it accomplishes nothing than just getting a stranger tell you what to do. I was like, "Since I'm depressed, I don't want to do anything, so how does that help?" Talking tends to be more effective on women, but everybody needs to vent once in a while, so it might help regardless. You could try
7 Cups and talk to a stranger who's there mostly to listen to you - but you can also find therapists there as well. If you don't want to do any of these things, try asking a friend to help you do that. Doing anything is hard under depression, so don't feel bad about asking for help, even if it seems insignificant.
Therapy isn't the only thing you can do. The best cures for depression are friendship, exercise and sunlight. Having a pet can also help alleviate depressive symptoms, as well listening to classical music (although I tend to find Mozart rather depressing so, eh, maybe skip that part). If you can crash at a friend's place/relative's place, this can help give you a fresher perspective. Environment does influence your mood, after all. These won't work instantly, of course, but can lessen feelings of hopelessness over time. If none of this is working, then you may have a chemical imbalance in your brain, which means it's time to get an appointment with a psychiatrist for medication.
I hope that helps.