Why my error message isn't appearing?

 <?php
  error_reporting('E_ALL ^ E_NOTICE');
 if(isset($_POST['reg'])){
   $fn = ucfirst($_POST['fname']);
   $ln = ucfirst($_POST['lname']);
   $un = $_POST['username'];
   $em = $_POST['email'];
   $pswd = $_POST['password'];
   $pswd2 = $_POST['password2'];
   
   $s=$db->prepare("SELECT email FROM userss WHERE username=:username");
   $s->execute(array(':username'=>$un));

   $q=$db->prepare("SELECT username FROM userss WHERE username=:username");
   $q->execute(array(':username'=>$un));
   
  if( $fn == "" ) {
  $er='Enter your First name';
}
elseif( $ln == "" ) {
  $er='Enter your Last name';
}
elseif( $un == "" ) {
  $er='Enter your username';
}
elseif( $pswd == "" ) {
  $er='Enter your password';
}
elseif( strlen($pswd) < 6 ) {
  $er='Password must be more than 6 characters';
}
elseif( $pswd != $pswd2 ) {
  $er='Password and confirm password does not match!';
}
elseif( $em != "" && !preg_match( "/^([a-zA-Z0-9])+([a-zA-Z0-9\._-])*@([a-zA-Z0-9_-])+([a-zA-Z0-9\._-]+)+$/", $_POST["email"] ) ) {
  $er='Enter valid email';
}
elseif($q->rowCount() > 0) { 
  $er = 'The username '.$un.' is already taken!';
} 
elseif($s->rowCount() > 0) {
  $er='The email '.$em.' is already registered, choose another!';
}
else{
  $pswd = password_hash($pswd, PASSWORD_DEFAULT);
  $stmt = $db->prepare("INSERT INTO users (username,first_name,last_name,email,password) VALUES (:username,:first_name,:last_name,:email,:password)");  
$stmt->execute( array(':username'=>$un,':first_name'=>$fn,':last_name'=>$ln,':email'=>$em,':password'=>$pswd));
 }
if ($stmt->rowCount() == 1) {
  header("Location:login.php");
} 
else {  
echo "error";
 }
}
?>

<form action="register.php" method="POST">
    <fieldset>
        <input type="text" style="margin-top:5px;" name="fname" id="fn" required="required" maxlength="15" placeholder="First Name"/><br />
        <input type="text" name="lname" id="ln" required="required" maxlength="15" placeholder="Last Name"/><br />
        <input type="text" name="username" id="un" required="required" maxlength="15" placeholder="Username" class="username" /><br />
        <input type="email" name="email" id="em" required="required" maxlength="35" placeholder="Email"/> <br />
        <input type="password" name="password" id="pswd" required="required" maxlength="15" placeholder="Password"/><br />
        <input type="password" name="password2" id="pswd2" required="required" maxlength="15" placeholder="Confirm Password"/><br />
        <input type="submit" id="submit" name="reg" value="Create an Account">
        <div id="er"><?php echo $er; ?></div>
  </fieldset>
  </form>