GCM notification not delivered immediately - php

Question

I developed a simple application in android just to send notifications from one user to other.as a quick overview of my app:
user register in the app using phone number.
in my database, a new record created contain the phone number and the GCM reg ID.
when the user try to send a notification to another user, the application will find the reg ID of the recipient in the DB and send a notification using a php code in my server.
My problem is most of times the notification didn't delivered to the recipient.
Java Code as I said, just search for the reg ID in the DB then submit it to the PHP server, and the PHP server when communicate with the GCM server.
PHP Code:
<?php
$con = mysqli_connect("localhost","username","my password","database name");
// Replace with real BROWSER API key from Google APIs
$apiKey = "my api key";
// Replace with real client registration IDs
$destinationcereg = mysqli_real_escape_string($con,$_REQUEST['destreg']);// this will provided by the app
$registrationIDs = array($destinationcereg);
// Message to be sent
$destinationcereg2 = &$destinationcereg;
// Set POST variables
$url = 'https://android.googleapis.com/gcm/send';
$fields = array(
'registration_ids' => $registrationIDs,
'data' => array( "message" => 'You Recieved New Message'),
);
$headers = array(
'Authorization: key=' . $apiKey,
'Content-Type: application/json'
);
// Open connection
$ch = curl_init();
// Set the url, number of POST vars, POST data
curl_setopt( $ch, CURLOPT_URL, $url );
curl_setopt( $ch, CURLOPT_POST, true );
curl_setopt( $ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt( $ch, CURLOPT_RETURNTRANSFER, true );
curl_setopt( $ch, CURLOPT_POSTFIELDS, json_encode( $fields ) );
// Execute post
$result = curl_exec($ch);
// Close connection
curl_close($ch);
echo $result;
echo ahmed;
?>
Also note that sometime the notification received after long time, most of times it's not received, and also sometimes it received immediately.
Can any one help me please ? Thanks in advance.