I didn't make any change at all and my CPC (cost per click) with adsense, in the past 2 days dropped from an average of $0.10 to $0.03... what can caused this?
The ads may be from a different advertiser or one that has bid less. I get this a lot when the higher advertiser bids daily balance is used up and the ads are shown for the next highest bids which result in lower payout.
also that new affiliate advertising rule has to have some effect , the new rule says that only the top bid for affiliate link advertisers gets shown for a particular keyword., so you won't see 3 or 4 affiliate link ads on a page anymore.
Change the content and keywords on your site. You should see different ads appear. Or go into Adsense and change the ad targeting to a similar but different category.