That's a bit weird, are you sure it's not an issue client side? I've never had an issue with PHP or MySQL - I'm not even sure if PHP does any caching by default.
You could try putting the following at the top of your scripts to prevent any browser caching:
php code:
<?php
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");
?>