Username always appearing as GUEST_NAME

Question

I have the following code but in place of the user name appears GUEST_NAME, even after logged in.
I have checked if I am using the correct table and used session_start();

MEMBERPAGE.PHP (where it appears GUEST_NAME):

<?php require('inc/config.php'); 
    print_r($_SESSION);

    //if not logged in redirect to login page
    if(!$user->is_logged_in()){ header('Location: login.php'); } 

    ?>
                    <h2>Member: 
                    <?php echo $_SESSION ['username'] ?></h2>

This is the result of: print_r($_SESSION);:

Array ( [last_log] => 1416320535
        [token] => ca6135136e3fa541d17b31af4ec66e1be05e187f
        [user] => 1
        [username] => GUEST_NAME
        [url] => /tvfootball2k15/en/members/main.php
        [loggedin] => > 1 )

INC/CONFIG.PHP

<?php
ob_start();
session_start();

//set timezone
date_default_timezone_set('Europe/London');

//database credentials
define('DBHOST','localhost');
define('DBUSER','root');
define('DBPASS','');
define('DBNAME','mydb');

//application address
define('DIR','http://domain.com/');
define('SITEEMAIL','[email protected]');

try {

    //create PDO connection 
    $db = new PDO("mysql:host=".DBHOST.";dbname=".DBNAME, DBUSER, DBPASS);
    $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

} catch(PDOException $e) {
    //show error
    echo '<p class="bg-danger">'.$e->getMessage().'</p>';
    exit;
}

//include the user class, pass in the database connection
include('classes/user.php');
$user = new User($db); 
?>

CLASSES/USER.PHP

<?php
include('password.php');
class User extends Password{

    private $_db;

    function __construct($db){
        parent::__construct();

        $this->_db = $db;
    }

    private function get_user_hash($username){  

        try {
            $stmt = $this->_db->prepare('SELECT password FROM members WHERE username = :username AND active="Yes" ');
            $stmt->execute(array('username' => $username));

            $row = $stmt->fetch();
            return $row['password'];

        } catch(PDOException $e) {
            echo '<p class="bg-danger">'.$e->getMessage().'</p>';
        }
    }

    public function login($username,$password){

        $hashed = $this->get_user_hash($username);

        if($this->password_verify($password,$hashed) == 1){

            $_SESSION['loggedin'] = true;
            return true;
        }   
    }

    public function logout(){
        session_destroy();
    }

    public function is_logged_in(){
        if(isset($_SESSION['loggedin']) && $_SESSION['loggedin'] == true){
            return true;
        }       
    }

}


?>

'Cause you keep showing up GUEST_NAME? How to return the username of the logged-in user?