Welcome to the forums!
Lots of things affect credit scores. A score drop doesn't mean that a "negative" item like a late payment has been reported.
The most likely thing is credit card balances changing. All kinds of things can happen with those to change your score. Likewise, an inquiry could have been reported. Your youngest account could have turned 1 year old, which in turn could have triggered something called "rebucketing." The possibilities are legion.
What you probably will want to do is learn more about how credit scores work. A good place to start would be this:
http://www.myfico.com/credit-education/credit-report-credit-score-articles/
You also may want to tell the folks on your thread what tool you are using to get your scores.
