what's your industry? You can PM me if you want. There's a possibility of a bidding war on the part of the advertisers and your keywords could have jetted in value. OR, sometimes the words displayed can change based upon the content even though the content shows the exact same for a month or more. and as it changes, some of the new advertisements may be more expensive.
If you can figure out which words are worth the most tho.... you might edit your content a bit to encourage those topics
