I have a Masters degree. I've worked hard for the past five years to get the credentials I have and yet I can't seem to find any job at which I could use my credentials or even one that is vaguely pleasant. Is it normal to be really depressed and feel alienated? I mean, I know anything anyone can say is to hang in there and something will come, but I feel like I'm positive nothing will. To add insult to injury, my MA is in the humanities.

This is no criticism of the Humanities and I also don't subscribe to those views that they are easy subjects as opposed to the sciences. I myself studied Mathematics and how many people do you meet who tell you that their job is a mathematician?
However, you have to dissociate your degree from your career. I hate Applied Maths and only really wanted to do Pure Maths. Even at 18, though, I knew that I'd probably end up working as an actuary. Now, I barely do any maths at all. And I don't earn anywhere near as much as an actuary. Life deals us some strange blows.
it doesn't work properly..
this is a typical issue of that incompatibility between supply and demand..
trust yourself and try to do something within what you already have