I too have a history of depression. And here is what I have learned to combat it. Do things. It doesn't matter what they are, do them. This will be my TL;DR for you. If you care to continue reading I have the following to say.
I think life is a series of moments. I am closing up on my twenty-fifth birthday. There have been so many moments in my life I regret, loathe, and make me wish I had never been born. I find it unempathetic when people tell you to get over it, naive when people tell you to find God, and at best you feel isolated and alone, at worst, people mock you pain. Depression isn't something you can hurdle in one bond and depression isn't something you can just paddle through if given an oar. No, depression is a crushing, lightless, Godless place like the depths of a great ocean and your ankle is tied to a stone. For many I think, including myself, even if you cut that stone of your ankle and make it afloat, you still feel like you can slide back under at any moment.
A little about myself. Currently, I'm in a happy relationship of 2+ years, I have a shaky, albeit, steady job, I am currently going to school to become a welder, and right now I feel like I am swimming to the shore. You wouldn't know it from first glance, but I have attempted to commit suicide. Especially early in my teenage years, it is all I would think about sometimes.
I'm not here to give you a sob story or compare my heartache to yours. But I know what it feels like. I know it hurts. I know you are looking at this colossal beast known as the future and it is terrifying and overwhelming and seemingly pointless to fight what you may feel is going to be a fate worse than death. It is a feeling, not a reality.
Now, here are a few tools I have used to uplift myself.
In case you would prefer yet another TL;DR, here is what I do: I aspire to be better than I am now. I ask myself, what makes me happy and unhappy, and I drop the baggage even to the extent of family members. I don't dwell on what if, I dwell on what can I do now. And I never let there be a need to left undone. These simple trains of thought are how I keep going, and how I stay sane. But if you allow me to ramble a little, maybe you might understand what I mean and perhaps crack a smile as I am sure to get less serious from this point on.
When I was just getting into the workforce, I had a string of fast food jobs, I was your stereotypical gamer guy who would rather be at home playing Halo and drinking mountain dew to my bladders content. Everyday seemed exactly the same. Wake up, go to school, come home, get the speech from my parents about what a lazy bum I was and that I needed to be ready to get out of the house by 18. This is when I was 15ish. At 17, I finally caved a started working at a job, let's call it Merry Cream. Not 6 months in to the job, I get fired, because I hated every minute of it and honestly, because I was just nine kinds of teenage lazy. All my parents had to say was that essentially, I was a fuck up, though in sane cordial conversation, my mother maintained, I was a late-bloomer. I graduated high school by the skin of my teeth, a 1.8 GPA despite blowing a preliminary ASVAB out of the water with a 76, a national average (or whatever the recruiter told me) of 89, and a name on that highest SAT scores banner.