ค่า Session ที่บันทึกลงใน database ไม่เปลี่ยนแปลง ต้องแก้ยังไงบ้างครับ

<?
@session_start();
include("paging.inc.php"); 

$user_day = $_POST['day'];
$user_mon = $_POST['month'];
$user_year = $_POST['year']; 
$Bday = $user_year."-".$user_mon."-".$user_day;

$strSQL = "INSERT INTO member (name,lastname,sex,date,address,tel,email,username,password,Status,SID,Active) VALUES ('".$_POST["name"]."' ,'".$_POST["lastname"]."' ,'".$_POST["sex"]."' ,'$Bday' ,'".$_POST["address"]."' ,'".$_POST["tel"]."' ,'".$_POST["email"]."' ,'".$_POST["username"]."' ,'".$_POST["password"]."','USER','".session_id()."','No')";
		$objQuery = mysql_query($strSQL);
		
		$member_id = mysql_insert_id();
	echo 'ลงทะเบียนสำเร็จแล้ว';		
		$strTo = $_POST["email"];
		$strSubject = "Activate Member Account";
		$strHeader = "Content-type: text/html; charset=utf-8\r\n"; // or UTF-8 //
		$strHeader .= "From: [email protected]";
		$strMessage = "";
		$strMessage .= "Welcome : ".$_POST["username"]."<br>";
		$strMessage .= "=================================<br>";
		$strMessage .= "Activate account click here.<br><br>";
		$strMessage .= "localhost/member/activate.php?sid=".session_id()."&uid=".$Uid."<br>";
		$strMessage .= "=================================<br>";
		$strMessage .= "admin.net<br>";

		$flgSend = mail($strTo,$strSubject,$strMessage,$strHeader); 
	mysql_close(); 

?>