What's the URL of your site? Beyond ad placement and things, AdSense is also going to be variable based on the types of topics being generated.
It's going to be a fine line about being too annoying and driving users away in the long run vs. not enough ads to generate enough revenue.
There are 2 things we did that drastically increased our ad revenue...
1. Throwing an ad into a random location INSIDE the post the user is currently reading. For example, look here... you will see an AdSense ad inside the first post. Reload the page and it moves.
http://forums.digitalpoint.com/showthread.php?t=2510990 This is the single biggest thing that I've found to exponentially increase AdSense revenue (we try to not annoy registered users too much, so only guests see it that way). We released an add-on to do it for XenForo:
http://xenforo.com/community/resources/digital-point-ad-positioning.232/ If you look at the
last comment in the discussion thread about it, the user is seeing 3x to 10x more ad revenue because of it.
2. This has nothing to do with AdSense, but when we started selling ads directly to advertisers, our overall ad revenue went up about 500% (without adding an extra placements), so I wouldn't ignore that. It just depends on if your site is popular enough that people are wanting to advertise on it directly. I ended up building a system to manage it all (that way it's all a hands-off [for me], self-help system for advertisers):
http://advertising.digitalpoint.com/ It became popular enough with advertisers just on digitalpoint.com that they were asking to use the system on their own sites, so I rebuilt it so other sites can use it too.