change the form tag:
<form action="" method="post" enctype="multipart/form-data">
to:
<form action="<?php echo $_SERVER["PHP_SELF"]; ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".$_SERVER["QUERY_STRING"]:""; ?>" method="post" enctype="multipart/form-data">