The economy as a whole isn't spending much on advertising right now and everyone's Adsense earnings are down. Theres tons of factors that can effect your adsense income, such as your niche, the time of year and some other things.
Make sure you pages are optimized as possible, you've got the best locations for your forums, and you're getting relevant advertisements delivered.
And i'm earning $xx.xx on my blog thats not even 2 weeks old