Problem with PHP, using load jquery + GET - php

Question

I'm currently doing a private chat (style messenger), and I got a problem..
I have a href a link which sends an ID using GET to another page, the thing is that on the other page I load a jquery script which again sends to another page, suddenly it no longer finds the ID GET, what should I do? I want to actualise the page (the messages) thanks (noted that I'm new, I'm not enough good to use ajax or something..)
message.php
message
<?php
// $allUsers = 'SELECT * FROM members WHERE name LIKE "%cc%" ORDER BY id DESC' / SEARCH MEMBERS
$allUsers = $dbh->query('SELECT * FROM members ORDER BY id DESC LIMIT 0, 5');
if ($allUsers->rowCount() > 0)
{
while ($user = $allUsers->fetch())
{
?>
<div id="s_un_main">
<div class="s_un_main_pun">
<img src="../images/avatar/<?php echo $user['avatar'];?>">
<p><?php echo $user['name']; ?></p>
</div>
<div class="s_un_main_pdeux">
<a class="private" target="_blank" href="private.php?id=<?php echo $user['id']; ?>">Message</a>
</div>
</div>
<?php
}
}
else
{
echo "<p>" . "Aucun utilisateur trouvé. " . "</p>";
}
?>
private.php
private
<div id="get_name">
<?php
// USERINFO
if (isset($_SESSION['id']) AND !empty($_SESSION['id']))
{
$getid = $_GET['id'];
$req = $dbh->prepare('SELECT * FROM members WHERE id = :getid');
$req->bindValue('getid', $getid);
$req->execute();
$userinfo = $req->fetch();
}
?>
<div>
<img id="img_header" width="50" src="../images/avatar/<?php echo $userinfo['avatar'];?>">
</div>
<?php echo "<p>" . $userinfo['name'] . "</p>"; ?>
</div>
<section id="zz">
<div id="show_msg">
<?php
// AFFICHER LES MESSAGES
$getid = $_GET['id'];
$takeMsg = $dbh->prepare('SELECT * FROM private WHERE id_sender = :sender AND id_receipter = :receipter OR id_sender = :senderr AND id_receipter = :receipterr');
$takeMsg->bindValue('sender', $_SESSION['id']);
$takeMsg->bindValue('receipter', $getid);
$takeMsg->bindValue('senderr', $getid);
$takeMsg->bindValue('receipterr', $_SESSION['id']);
$takeMsg->execute();
while ($message = $takeMsg->fetch())
{
if ($message['id_receipter'] == $_SESSION['id'])
{
?>
<p style="color: red"><?php echo $message['message']; ?></p>
<?php
}
elseif ($message['id_receipter'] == $_GET['id'])
{
?>
<p style="color: green "><?php echo $message['message']; ?></p>
<?php
}
}
?>
</div>
</section>
<form id="private_form" method="POST" action="">
<textarea name="message"></textarea>
<input type="submit" name="send"></input>
</form>
<script>
setInterval('load_messages()', 1500);
function load_messages()
{
$('#zz').load('private_message.php');
}
</script>
private_message.php
error
<!-- DB -->
<?php include("../db/db.php"); ?>
<!-- DB -->
<?php
// AFFICHER LES MESSAGES
$getid = $_GET['id'];
var_dump($getid);
$takeMsg = $dbh->prepare('SELECT * FROM private WHERE id_sender = :sender AND id_receipter = :receipter OR id_sender = :senderr AND id_receipter = :receipterr');
$takeMsg->bindValue('sender', $_SESSION['id']);
$takeMsg->bindValue('receipter', $getid);
$takeMsg->bindValue('senderr', $getid);
$takeMsg->bindValue('receipterr', $_SESSION['id']);
$takeMsg->execute();
while ($message = $takeMsg->fetch())
{
if ($message['id_receipter'] == $_SESSION['id'])
{
?>
<p style="color: red"><?php echo $message['message']; ?></p>
<?php
}
elseif ($message['id_receipter'] == $_GET['id'])
{
?>
<p style="color: green "><?php echo $message['message']; ?></p>
<?php
}
}
?>
var_dump($id) = not found