You can use channels. Make each channel for different website, and then you can track the amount of clicks and earnings from each channel seperatly.
when you generate your adsense code, save that as a channel and name each channel in a way so that you can remember for which site the channel is. for example, if you have a site for health and have adsense on the top and on sidebar, then you can name the channels like health-top and health-side that way you not only know which site the clicks are coming from but from which ad units
When creating your ads, you can add your ads to 'channels'. Channels are groups that you create to track your statistics for your ads. You can make them under Manage Ads. Hope I've helped.