PHP ve Ajax ile Live Chat yaparken sayfa yenilenince mesajlar tekrardan veri tabanına gidiyor

function sendMessages() {
            $.ajax({
                type: 'POST',
                url: 'sent_messages.php',
                data: {
                    user_id: user_id,
                    session_name: session_name,
                    session_id: session_id,
                    text: text,
                },
                success: function(response) {
                    if ($('#chat2').html() !== response) {
                        $('#chat2').html(response);
                        keepScrollBarDown();
                    }
                }
            });
        }
    sendMessages();
   


sentMessages.php sayfasından kodlar
<?php
include 'db.php';
$sender_message=$_POST['text'];
$sender_id=$_POST['session_id'];
$receiver_id=$_POST['user_id'];


if($sender_message!=null)
{
    $query = "INSERT INTO messages (sender_id, receiver_id, sender_message) VALUES ('$sender_id', '$receiver_id', '$sender_message')";
    $query2 = mysqli_query($db, $query);
}
 

?>