jQuery, Ajax, SQL Pagination, problems with SESSION

This is my first time doing pagination with jQuery ajax. I do it like this:

I include file 'GetAllMessages.php' into a div, only if i'm logged in.[works]

I include file 'GetMessages.php' again only if im logged in which tells me how many messages are in database.[works]

When I click on my 'messages' link I open a popup and I get my first four messages from 'GetAllMessages.php'.[works]

At the end of this div i have pages like [1,2,3...] and then with jquery $.ajax function (post method) i go again into 'GetAllMessages.php' but this time I tell the file which page I clicked so it gives me the messages I want next.[doesnt work]

It's like SESSION does not exsist, but if I add 'SESSION_START' at start in 'GetAllMesasages.php' it says its already started on my initial 'GetAllMessages.php' load, but when I click on page link[1,2,3...] the error goes away and it all works.

GetAllMessages.php

<?php
if(isset($_SESSION["uname"])){
include ('config.php');
include ('getMessages.php');
$pages=$messageCount/$messagesPerPage;
if(isset($_POST["page"])){
$page=$_POST["page"];
}else{
$page=1;
}
$startQuery=($page-1)*$messagesPerPage;
$getMessagesQuery = "SELECT * from messages ORDER BY id DESC LIMIT ".$startQuery.",".$messagesPerPage."";
$result = $conn->query($getMessagesQuery);
if($result->num_rows>0){
    while($row=$result->fetch_assoc()){
        $mId=$row["id"];
        $mName=$row["name"];
        $mEmail=$row["email"];
        $mMessage=$row["message"];
        $mDate=$row["messageDate"];
        $mIsRead=$row["seen"];
        $mIsAnswered=$row["answered"];
        if($mIsRead==0){
            $messageStatus="unread";
            $markReadButton="<button class='button1'>Mark as read</button>";
        }else if($mIsAnswered==1){
            $markReadButton="";
            $messageStatus="answered";
        }else{
            $markReadButton="";
            $messageStatus="";
        }                       
        echo "
        <div class='message ".$messageStatus."' data-messageid='".$mId."'>
            <p class='date'>".$mDate."</p>
            <p class='sender'>".$mName." - ".$mEmail."</p>
            <p class='messageContent'>".$mMessage."</p>
            <span class='buttons'>              
            <button class='reply'>Reply</button>
            ".$markReadButton."
            </span>
        </div>";
    }
}
}else die();
?>