используйте http_build_query
$data = array('foo'=>'bar',
'baz'=>'boom',
'cow'=>'milk',
'php'=>'hypertext processor');
echo http_build_query($data) . "\n";
echo http_build_query($data, '', '&');
?>
The above example will output:
foo=bar&baz=boom&cow=milk&php=hypertext+processor
foo=bar&baz=boom&cow=milk&php=hypertext+processor
для вашего случая
$get_data=$_GET;
echo http_build_query($get_data) . "\n";
echo http_build_query($get_data, '', '&');