easier said than done anon when you can't even talk yourself into eating since even that takes too much effort. your advice, when it can work, does help. doing things helps, but mostly because you're just distracting yourself. exercise does have a proven effect, and diet as well. the best advice though is to seek medical professional help. sometimes this doesn't help either as the medication isn't effective, or they refuse to prescribe the medicine to you, or healthcare won't cover it, or your psychiatrist is a nutcase themselves, or you slip up on your wording and end up in 72 hour hold (in US at least).
depression is hard. best to just try and take things day by day and realize that everything is temporary, at least that's how I do it.