get infos of member on php - php

Question

i have two page :
login.php :
<form action="conn.php" method="POST">
Username:
<input type="text" id="username" name="username" />
Password:
<input type="password" id="password" name="password" />
<input name="submit" id="submit" type="submit" value="Login" />
</form>
And the PHP
<?php
$success = "";
if(isset($_POST['submit']) == "Login" )
{
$username = strip_tags($_POST['username']);
$password = strip_tags($_POST['password']);
$error = array();
// Username Validation
if(empty($username))
{
$error[] = " Empty or invalid username ";
}
if(empty($password)){
$error[] = "Enter your password";
}
if(count($error) == 0){
$host = 'localhost';
$database_name = 'projett';
$database_user_name = '';
$database_password = '';
$connection=new MongoClient();
if($connection){
// Select Database
$database = $connection->$database_name;
// Select Collection
$collection = $database->reg_users;
$user_data= array("username" => $username,"password" => md5($pass));
$result = $collection->findOne($user_data);
if($result){
$success = "You are successully loggedIn";
header("Location: Articles.php");
}
} else {
die("Mongo DB not installed");
}
}
}
?>
i want display on Member.php the username of the member but when he complete login form a new page open(article.php) with his username