I've had similar problems, it's a vicious circle as the best 'cure' as told me by a good therapist is simply keep yourself busy when you begin feeling down but the problem with that is when you're down you don't feel like doing anything and that leaves your mind idle and you begin concentratiing on what's made you depressed and then that's all you can think about. I don't think there's a total cure unless your depression was brought upon by a specific cause like reaction to a death or illness which can improve in time, in fact expecting a total cure can get you more down as you begin to realise that it's a position you can never reach. As hard as it is you have to remain positive as life could change overnight and you could be loving life in a years time, just keep your mind off negative thoughts and do things that improve your life and not add to your bad feelings. Like most depression sufferers you will get days when you feel more positive and energetic, use those days wisely and maybe start a business, hobby, exercise regime or make new friends as these things will still be going on days when you feel down and you may find the days you feel down becoming less and less. I've got my own business and although it won't make me a millionaire and can drive me crazy sometimes it gives you something to focus on 24/7 and sometimes that's the best you can hope for.
I also found weirdly enough that others find me good to talk too (when you're depressed your self esteem is low and you think you're no good to anyone) and a lot of people begun telling me their problems and happy someone wanted to know how they were and willing to give them time, you'll feel more positive about yourself as you're useful to others even if feel you are not to yourself and i'm sure this causes chemical changes to the brain along with things like exercising etc and this can be a 'natural' cure for depression.
