Best advice I can give is to just do some exercise. I don't know why, but the 1-2 hours I spend running is always the best part of my day. There's always something outside that makes me smile a bit, most of it being animals doing random things. It's so easy to hate exercise and running, but at the same time it's so easy to get addicted to it. I don't know why, but exercise always makes me feel a lot more positive, and there are studies that demonstrate the benefits too.
I think I mostly chalk up the effects of exercise to living unnaturally. Humans were built to be distance runners, not to live on a computer and spend several hours a day forcing information into our heads. If we were mentally encoded to live in the Rift Valley to persistence hunt animals and we come to live indoors purposelessly obsessed with computers, then I feel like something is bound to go wrong. I believe this is the reason for the slight suicide epidemic in the US, though I would advise you to use your own understanding and to formulate your own opinions. (Rely on information given from medical studies, not message boards!)
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https://www.ncbi.nlm.nih.gov/pubmed/21658349
TL;DR: Exercise in it's own right is so effective that it could be considered somewhat of a treatment option for depression
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