Hmmm...
Depending on how you access the page again (back-button?), this may be a result of the browsers caching.
Try this to prevent the browser from caching your page:
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
header("Cache-Control: no-cache, must-revalidate");
header("Pragma: no-cache");
For the second problem:
A way to avoid double inserts is to do them on top of script (before any output), then relocate the client back to the same page:
## Do inserts here ##
## Relocate ##
header("Location:".$_SERVER['PHP_SELF']."");
## Output page & result ##
knutm