I'm having a similar problem, but my site is only 1 month old. I'm no going to sweat it though, I'm just going to keep building the pages it still needs and a few web2 backlinks and revisit it back in a few months.
The last thing you want to do is let this one site distract you from your next. You can be beating yourself up trying to figure out whats wrong with it and spending to much time trying to get it to rank and then 4-6 months down the road you start ranking for some long tails and start earning a decent amount. You'll be kicking yourself if you wasted all this time just on this one site when rankings where going to be inevitable then you start on the next project and have to go through the whole process again.