This has also happened to me. Last week my website traffic doubled and revenue from clickthroughs is now two times less. Its really depressing to see your traffic doubling but your revenue staying the same. My earnings per click went down almost in half. I've noticed that generally, days with high click-through rates also have low earnings per click, while days with lower click-through rater have higher earnings per click. It's a rare day indeed when I get both high clicks AND high earnings