Push Notification, OnMessageReceived triggers multiple times, loading multiple pages.

Guys im having an issue,

I want to load a page that displays the push notification string content but the OnReceivedMessage() gets triggered an increasing number of times equal to the amount of times I go to the DisplayNotificationPage and back.

So first time I run, the OnRevceivedMessage triggers, opens the DisplayNotificationPage() that i close and return to the previous page through PopAsync(). The second time the OnReceivedMessage() triggers twice, then 3 times etc for every run.

What is going on? I think it has to do something with subscribing.. how can i fix this?

[XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class NotificationReceivingPage : ContentPage
    {
        public NotificationReceivingPage ()
        {
            InitializeComponent ();
        }


        protected override void OnAppearing()
        {
            base.OnAppearing();
            MessagingCenter.Subscribe<object, string>(this, App.NotificationReceivedKey, OnMessageReceived);
        }

        private void OnMessageReceived(object sender, string incomingNotificationBody)     // gets triggered x1, x2, x3... and so on
        {
            if (!string.IsNullOrEmpty(incomingNotificationBody))
            {
                Navigation.PushAsync(new NotificationDisplayPage(incomingNotificationBody));
            }         
        }

        protected override void OnDisappearing()
        {
            base.OnDisappearing();
            MessagingCenter.Unsubscribe<object>(this, App.NotificationReceivedKey);
        }


[XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class NotificationDisplayPage : ContentPage
    {
        ISimpleAudioPlayer soundPlayer;
        private static string incomingMessage = null;

        //default constructor
        public AlarmDisplayPage ()
        {
            InitializeComponent ();
        }

        // overloaded constructor that receives incoming notification body
        public AlarmDisplayPage(string messageBody)
        {
            InitializeComponent();

            if (messageBody != null)
            {
                incomingMessage = messageBody;
            }

            //alarm to sound on incoming message
            var assembly = typeof(AlarmDisplayPage);
            alertHeader.Source = ImageSource.FromResource("SApp.Assets.Images.mypic-header.png", assembly);
        }


        protected override void OnAppearing()
        {
            base.OnAppearing();

            stopAlarmButton.IsEnabled = true;

            //initialize soundplayer
            soundPlayer = Plugin.SimpleAudioPlayer.CrossSimpleAudioPlayer.Current;
            soundPlayer.Load(GetStreamFromFile("mysound.mp3"));

            if (!string.IsNullOrEmpty(incomingMessage))
            {
                setEventDetails();

                //play the alarm
                soundPlayer.Play();
            }    

        }

        protected override void OnDisappearing()
        {
            base.OnDisappearing();
            soundPlayer.Stop();
            incomingMessage = null;
        }


        private Stream GetStreamFromFile(string mediaFilename)
        {
            var assembly = typeof(App).GetTypeInfo().Assembly;
            var stream = assembly.GetManifestResourceStream("SApp.Assets.Sounds." + mediaFilename);
            return stream;
        }

        private void stopAlarmButton_Clicked(object sender, EventArgs e)
        {
            stopAlarmButton.IsEnabled = false;

            Navigation.PopToRootAsync();
        }

        private void setEventDetails()
        {
            if (!string.IsNullOrEmpty(incomingMessage))
            {
                labelEventType.Text = incomingMessage;
            }
            else
            {
                labelEventType.Text = "No Data";
            }

        }
    }