Hang in there, and keep practicing your craft. If the goal of a big published novel seems too daunting, you might want to get there by setting some smaller goals and working your way up. There are many areas where it can be easier to get published than writing a whole book. Getting something done there, even if it doesn't get the attention of editors for books, is at least a way to practice your writing and improve.
The first level is nonpaying markets. For example, fanzines and fan websites. These don't pay any money, but you will at least need to write something that is long enough to be an article and that will please the editor putting the website together. If you're really lucky, you may write something that gets turned into an anonymous Internet forward. This isn't going to help your writing career, but it can be a real ego boost.
There are also websites that are technically paying markets, but pay very little. Associated Content is one that is talked about pretty often, and pays maybe $30 per article if you're lucky. Sure, that's not likely to be enough to live on, and it's nowhere near what you would make if you moved up the scale. But it's easier to get accepted there.
Next up the scale is magazines. Many of them buy freelance articles for several hundred or even a thousand dollars (Come to think of it, that's probably more than your average
PublishAmerica book earns). Some people even work full time at writing freelance articles. An article may be under 2,000 words, much easier to write than a full book. They also pay real money, and will get respect from agents and editors if you are looking to sell your book. So if you want some practice at real, professional writing, but aren't sure if you can commit the time to writing a whole book, try a few magazine articles.
So if you're feeling like your goal is too big, you might want to break it down into steps to build your writing career. Such as maybe "I'll write a few articles for fan sites to build my confidance and practice writing something short. Then I'll see if I can turn pro by selling articles to paying websites or magazines. Once I feel certain I can write, I'll sit down and write a book."
Good luck.