I am having Adsense account for past three years.At first I used to get $100 to $150 per month for one or two sites.But now I am having few sites with good traffic.But not able to earn inorder to fulfill even my hosting price.
Have you maximize your adsense to its maximum ? Blend it well to get more clicks and filter the ads to get higher CTR. My sig for details on ads filtering
Try looking for another network, after my site dropped to 1$ eCPM I am using it as a 3rd tier network. Because there are a lot better networks who can pay 2$ CPM per 300x250 banner.
How many ads do you have per page and what is the placement? You could force the clicks a bit, I guess, if you want more revenue.