the last else if statment wont wont work it's like there's is nothing there

the last else if statment wont wont work it's like there's is nothing there and i can't figure out why

<?php

if (isset($_POST["submit"])) {

      require 'db.inc.php';

      $username = $_POST["username"];
      $email = $_POST["email"];
      $password = $_POST["password"];
      $confirme = $_POST["confirme"];

      if(empty($username) || empty($email) || empty($password) || empty($confirme)) {

        header( 'Location: ../signup.php?error=empty&usern=' . $username .  '&mail='  . $email );
        exit();
      }
      else if(!filter_var($email, FILTER_VALIDATE_EMAIL) && !perg_match('/^[a-zA-Z0-9]*$/', $username)) {

        header( 'Location: ../signup.php?error=invalidmailusern');
        exit();
      }
      else if(!filter_var($email, FILTER_VALIDATE_EMAIL)) {

        header( 'Location: ../signup.php?error=invalidmail&usern=' . $username );
        exit();
      }
      else if(!perg_match('/^[a-zA-Z0-9]*$/', $username)) {

        header( 'Location: ../signup.php?error=invalidusern&mail=' . $email );
        exit();
      }
     else if (true) {
       // code...
       header( 'Location: ../signup.php?error=empty&usern=' . $username .  '&mail='  . $email );
       exit();
     }

}