I experience the same thing with AdSense, some days I make more than others.

As was mentioned, concentrate on your content and the visitors will increase, and hopefully your adsense dollars.

__________________
Confused about technology? Technically Easy has the answers!

How I Converted from Blogger to WordPress
Do You Quit Too Early?
Using Google Alerts to Track Copies of Your Web Content
Viewing Your Web Site in Many Browsers with Browsershots