Login script issue with database

I wrote a login script for a website that I am building using resources I have found online. When I ran my code on a local server it worked fine but now that I am actually running it online on a real server it doesn't work. I think I have narrowed down my error but with being new to PHP and not having prior experience with MySql I can't really fix my problem. This is the file for the login script:

  //login file
<?php
class Login{
    private $db_connection = null;

    public function __construct(){
        session_start();
        $this->dologinWithPostData();
    }

    private function dologinWithPostData(){

             $this->db_connection = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME);

            if (!$this->db_connection()->connect_errno) {

                // escape the POST stuff
                $email = $_POST['email'];
                // database query, getting all the info of the selected user (allows login via email address in the
                // username field)
                $sql = "SELECT email, password
                        FROM users
                        WHERE email = '" . $email ."'";

                $result_of_login_check = $this->db_connection->query($sql);//This is 0

                // if this user exists
                if ($result_of_login_check->num_rows == 1) {
                    // get result row (as an object)
                    $result_row = $result_of_login_check->fetch_object();
                    // using PHP 5.5's password_verify() function to check if the provided password fits
                    // the hash of that user's password
                    if ($_POST['password'] == $result_row->password) {
                        // write user data into PHP SESSION (a file on your server)
                        $_SESSION['email'] = $result_row->email;
                        $_SESSION['user_login_status'] = 1;
                    } else {
                        $this->errors[] = "Wrong password. Try again.";
                        $_SESSION['user_login_status'] = 0;
                    }
                } else {
                    $this->errors[] = "This user does not exist.";
                }
            } else {
                $this->errors[] = "Database connection problem.";
            }
        }

    print_r($this->errors);
    }

    public function isUserLoggedIn()
    {
        if (isset($_SESSION['user_login_status']) AND $_SESSION['user_login_status'] == 1) {
            return true;
        }
        // default return
        return false;
    }
}

?>

I run it in another file that is essentially the following:

//Run file
require_once("dbconfig.php");
    include_once("login.php");
    $login = new Login();
    if($login->isUserLoggedIn() == true){
    //go to another page }

The variables used to access the database are instantiated in dbconfig.php and are correct. With this code I get an error that says the page is not working and is unable to handle the request. When I comment out the line

if (!$this->db_connection()->connect_errno) {

and the else statement following it, the output is "This user does not exist". So I think the error has something to do with $this->db_connection()->connect_errno). If you can find where I went wrong or have any advice on how to rewrite the script to make it better, it is greatly appreciated.