I Have Dysthymia

Is this really an illness or just a hard-wired personality trait? I've been like this my whole life, but every few years I really spiral into what I've learned is called "double depression." 10 years ago, on the brink of suicide, I went to see a therapist who diagnosed me as dysthymic. (It's now called PDD.) I wouldn't have believed in any diagnosis, except she described me to to a T. I thought (and still do think) that people are lying when they say they enjoy life. Optimistic or "happy/peppy" people are only pretending. Get to know anyone well enough and you'll see their pain. At the same time, I've had roommates over the years and marveled at their ability to get up every day, every single day, not feeling completely drained and miserable about the day ahead. I can't imagine that it's possible to just get out of bed in the morning without any struggle. I can't understand how it's possible that others don't feel an existential pull in the other direction--away from life instead of toward it. I think about suicide every single day, yet I'm still here. The only fortunate thing is that I don't rely on happiness or even contentment to keep going. If I did, I'd have ended it along ago. I have some routines that I try very hard to stick to. I focus on keeping things clean and in order. I try to do my best at whatever I do. I try to be the best sibling, child, friend, employee, that I can be. I've try out different kinds of treatments (yoga, meditation, exercise, supplements, talk therapy, rolfing, massage, acupuncture, antidepressants, self-hypnosis, diet, volunteering, social meetups, personal development classes and activities) yet none of it makes me feel pulled toward life. well, this is my cry for help. if anyone out there gives a shit.