I'm so frustrated still to be in the mental hospital

First of all: I am having a really bad day, which of course has a big influence on my thoughts.
It's very frustrating to be committed to the mental hospital, I don't really feel any better, no progress at all.
The nurses and my mom tries to talk me out of my worries, more or less successful.

How do they know, that this medication will work(?) The last apparently didn't, so why did they choose this new medication for me - why not another one(?)...

Shouldn't there be some kind of test or something, that would at least give an idea of what kind of mental disease a patient has - and what kind of treatment that would be best (?)
Like a Rorschach inkblot test, a questionnaire, or something...
I'm getting very impatient here, this does not really lead in a good direction in my opinion. Now we will "try" this new medication for a while... Try!
Well that's just great, cause most of the depression medication they give us, takes 3-4 week or more to kick in with full effect. So if this doesn't seem to work, it's yet another month for the patient to wait and see, if the new drug will take effect.
Aren't we in 2011(?) Where 25% of all people in one point in their lives unfortunately suffer from depression and/or anxiety. I cant believe, that there's no way to test us, for what kind of medication, that would help us.

How does the doctor decide then(?) By throwing dices(?) Looking at the weather report(?)

I mean no disrespect for the doctors around the world - I just have difficulties with the fact, that there's apparently no "tools" to find the correct medication for such a common mental problem, like depression/anxiety.

Picture posted under creative commons license by: Dwayne Coleman