form validation with ajax, php, and mysql

I'm building a login form and want to instantly check to make sure the email address is one that's in my database.

I've looked around and tried a bunch of different things to make this work, but I can't seem to get this working correctly.

Here's the Form

<form>
<input type="text" id="email" name="email" placeholder="Email Address" onblur="checkEmail(this.value);" onchange="checkEmail(this.value);"/>
<input type="password" id="password" name="password" placeholder="Password"/>
<input type="button" id="login-signup" value="Login / Sign Up"/>
</form>

Here's the Javascript. This is where I think the problem is.

function checkEmail(email) {
    // check to see if the email exists in the database using PHP and MySQL
    $.ajax({                                      
        url: 'login.php',               //the script to call to get data 
        type: 'post',  
        data: {
            email: $('#email').val()
        }, 
        dataType: 'json',               //data format      
        success: function(response) {       //on reception of reply
            if(response == 'match') {
                console.log('match');
            } else if (response == 'no match') {
                console.log('no match');
            } else if (response == 'error') {
                console.log('error');
            } else {
                console.log('who knows');
            }
        } 
    });

}

And here's login.php If I navigate to mywebsite.com/login.php?email=email then everything works correctly, so I know this is doing what I need it to. I imagine the problem is in my ajax

$db_host = "host";
$db_user = "user";
$db_pass = "pass";
$db_name = "name";


$db = new PDO('mysql:host='.$db_host.';dbname='.$db_name, $db_user, $db_pass);


if(isset($_GET['email'])) {
    $email = $_GET['email'];
    echo $email;
}

// Using prepared statements almost eliminates the possibility of SQL Injection.
$preparedQuery = $db->prepare("SELECT * FROM `members` WHERE `email` = :email");
$preparedQuery->bindValue(":email", $email);
$preparedQuery->execute();

// Retrieve the results from the database
$user = $preparedQuery->fetch(PDO::FETCH_ASSOC);

// If there is a user record print the user & pass... 
if($user != ''){
    echo 'match';
    $_SESSION['email'] = $email;
} else if ($user == '') {
    echo 'no match';
} else {
    echo 'error';
}