What sort of site does Google approve for Adsense?
The key is to have a unique and compelling site. Just because your posts are original does not mean they are unique and compelling. You site needs to offer something that no other site offers. Advertisers do not want to pay for adverts on lower quality sites.
Here is a good example: In my spare time I try to do some running and am aware of some of the issues in the running community and was recently searching for some info on one of those issues. I came across this site. Have a look at it. Look at the content. From my perspective, the content is compelling, readable, almost witty, but most important it is unique and the spin that the blogger takes can not be found anywhere else. I also recognize a couple of the names that appear in the comments section of some of the posts – they are well known and prominent people in the industry! What does that say about this blog? This is the sort of site that people would really want in their search results. If you were paying for Adwords in that niche, would you want your adverts to appear on that site via Adsense?