I wrote my first book and, after some advices, I decided to look for an agent. Most of them never replied. Some of them said they didn't work with unpublished writers. One of them, replied in a few days and sent me a contract. Of course I asked him how he could send me a contract if he didn't have the time to read the manuscript and know if it was good. Then he said he would read and never came back.
I only had lucky when I start to try publishers directly and, even so, I can't say how many copies of my manuscript and I sent without receiving a single answer. I know it only passed a month since I started to contact agents and publishers but, the wait drivers you nuts. The good thing is that I received a positive answer and a negative one, and that means -- at least to me -- that it's perfectly possible to publish without an agent.
I'm still waiting for some replies, and I know they will come. A month is a very short time for answers from a publisher. Like you, I believe in my project so I decided to wait a little longer.
The truth is that agents are somewhat like publishers. They are more prone to invest on a famous person then to bet in a new writer. You may say this is absurd but, sometimes it's better to be safe then sorry. There are a lot of writers around and -- at least in Portuguese context -- more manuscripts than publishing opportunities.
Agents will need to invest time in their writers. An agent will help the writer in a lot of things, not only delivering the manuscript to publishers. If they represent countless writers, they won't be able to do it right with none of them... Or, at least, with some of them. They need to pick the ones they think are most promising.
Remember this is business. You may love your manuscript like your own son, but this is all business.
But, then again, comes the problem: there are a lot of writers around and more manuscripts than publishing opportunities. Sometimes agents and publishers just won't pay enough attention to see potential; or sometimes they see a wonderful book but not something they can easily sell; if that happens, they will refuse you, even if you are good. If you believe in your project, you should keep trying. Not only with agents, but with publishers directly. I don't like self publishing so, I won't say that's the way.
Also, try to find and learn what are the best ways to approach publishers and agents. Sometimes they refuse works because the writer doesn't know how to contact them. For example, sending fantasy books to a crime fiction publisher; or demanding too much on a first approach; etc...
Also start a blog and make yourself known. Go to literary events and talk to people. I remember some girl who shared a book in a free site and, after I don't know how many downloads (it was a lot) a publisher contact her to print the book. I also remember a lot of guys who were bloggers and published only because they had a captive public (their blog followers).
Well, there's no magical trick. I'm in the same boat as you are and I'm doing almost the same thing as you are so, I'm telling you what I learned during the process. In a few months I will be able to say if the results came but, until there, maybe somebody else here can provide better tips than the ones I gave to approach agents and publishers.