I was making a solid X a day on my website, which displays mostly webhosting banners. That X was very good, about three or four times what I used to make before the webhosting banners started appearing. But today, (according to my calculations) I'm making X/3. The banners on the website are still the very same, so I ask you guys? WHY?
Well, there are *lots* of variables.. are you getting less traffic than before? Did you drop in the SERPs? Maybe people are now bidding less for the ads you're showing. etc.
Do not worry about daily earnings. IMHO only monthly summary indicates how good you are comparing to prev. months. And a content topic also plays a role here. Some months can be hot and other ones are slow for different topics...