I really hate when people say the "you're beautiful" part to try and imply that should make you feel better. I mean, no one says it to me... but the thing is, when they say it to you what does that imply? That if you weren't beautiful then fuck you? That non-beautiful people somehow deserve pain and it's okay if they die? IF you are someone, like you seem to be, who cares it makes you think about this sort of stuff and makes you doubt if the doctor really gives a crap. Maybe if you stopped being beautiful your value goes away and no one cares? I think it's bad precedent for doctors in particular to say that kind of shit to someone suffering.
My point here is... and I know it doesn't exactly help you... but, doctors are just people like everyone else. Maybe they had some more school or whatever, but IF they knew everything, or even a lot of anything, then there wouldn't be many depressed people would there? It's a whole lot of trial and error and they'll mess around with medicines for you if they are psychiatrists rather than psychologists... but in the end, they have their own problems too and can't fix themselves. IF they knew how to fix you, wouldn't they fix themselves?
A doctor who knows how to put on a cast for a broken bone, for instance, could do it to themselves except for needing an extra hand and better angle... but they know the procedure. Mental illnesses are not in the same league as physical ones, and nobody really really knows why a lot of us think or feel or are different.
So you do have to take care with how much you are free with doctors who wield power to lock you up... and I caution against putting all your faith into them solving your problems and more than you would anyone else you confide in to solve them. It is true that in the end we kind of have to solve our own problems... and some of us can't do that... and some of us maybe even can't be helped.
The positive thing I'll try and say here, though... is if you are having back and forth... ups and then downs... I feel like there's hope for you more than you might feel at the moment. I don't have ups... just differing degrees of down. But if you have ups, that's to me a sign you might have reason to be hopeful and pay attention to that. Give yourself a fair chance, especially since you are only almost barely 20. I know the world can be harsh and cruel and crappy and it can seem like there's no way out... and that's kind of where I am at 55 years old... but when I was your age, I still had hope... and for many people that hope pays off... so I really hate to see young people not give themselves a chance.