I have the same thing on my forums with ads like that. The problem is the google adsense spider can't sign into your forum so it can read the content of the page so they have no idea what to add. Any page that is veiwable to guest the spiders can read, hope that helps.
As for you ads in posts. If you want more ads just repeat the code and if you want it to show up in different post just use something like 1,3,5 or whatever spacing you want.