Does your school have a career center? It might be helpful to have someone look at the resume and cover letters you've been sending. If the field is new to you there might be things you're not saying quite the right way, or things you should be playing up more than you are... every industry has its own quirks and it's enough to drive you nuts. I've had job hunts where I change a couple words and all of a sudden I get call backs.
Not trying to be too prescriptive. I've gone through some pretty tumultuous career stuff over time and I understand how bad it can feel.