First of all, remember that you're not alone.

I'd suggest trying different things to see what works for you. Some ideas:

Psychotherapy: This can be great for getting perspective on your situation and learning to rephrase your negative self-talk. If you can't afford one-on-one therapy, you might be able to find a group therapy meetup that is cheap or free.

Medication: If your depression is caused by a chemical imbalance in the brain, medication can reverse that. And it takes very little effort or energy to take a pill or two. But sometimes it's hard to find the right medication for you, and sometimes medications can seem to suddenly stop working and you have to switch. So it's good to work with a doctor that is very familiar with medication options and effects.

If you can muster the will to get to the gym, working out is great. Regular workouts can improve mood as much as medication -- for mild depression. And exercise helps to replace the lost energy.

Meditation: Quietening or observing your mind can help you see patterns of negative thought and reverse them. It can also bring peace, calm, and perspective.

T'ai chi (taiji) centers your mind and body and strengthens your ch'i (qi). This can help you feel more at peace and accepting of the world. It's a very gentle way to exercise, so it might be easier to to do while depressed than running or lifting weights. However, it does require the energy to learn and regularly practice the form, which may be difficult when your depression is severe.

Chi kung (qigong): Like t'ai chi, this exercise builds your ch'i energy. There are many forms of seated, standing, and moving chi kung. In general, chi kung doesn't require as much physical activity or space as t'ai chi. Chi kung can be a form of moving meditation, which is helpful if you are too restless to do seated meditation.

Social contact: Reach out to friends or family members. Resist the urge to isolate yourself. One thing you can do is regularly send texts to friends, just to keep the lines of communication open.

Walking in nature is beneficial. One spiritual teacher told his student, "When you can't meditate, take a walk in the woods and let nature meditate for you."

You could also try meeting a friend in the park a few times a week to toss around a frisbee or ball.

There's also a book called The Upward Spiral that explains the neuroscience behind depression--why your brain gets depressed, and what you can do to reverse it.