Android Notification Update Periodically Silently Not Working (Handler issue?)

Working on my first android app so I am a complete noob so I'm probably making a silly mistake but I cannot get the notification text to update periodically. It works if I reclick the toggle button but I want the notification to update automatically if the week number has changed and to refresh the notification silently. Included a snippet of my code, thanks for the help in advance.

import android.app.NotificationManager;

import android.content.Context;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.support.v7.app.NotificationCompat;

import android.util.Log;

import android.os.Handler;

import android.widget.CompoundButton;

import android.widget.ToggleButton;



import java.util.Calendar;



public class MainActivity extends AppCompatActivity {



    private static final String TAG = "MyActivity";





    public void createNotification() {



       final Calendar now = Calendar.getInstance();

       now.get(Calendar.WEEK_OF_YEAR);



       int weekId = 1;

       final NotificationCompat.Builder nBuilder = (NotificationCompat.Builder) new NotificationCompat.Builder(this)

               .setContentTitle("Week")

               .setContentText(""+now.get(Calendar.WEEK_OF_YEAR))

               .setSmallIcon(R.drawable.ic_stat_name);

       final NotificationManager NM = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

       NM.notify(weekId, nBuilder.build());



    }



    // Init

    private Handler handler = new Handler();

    private Runnable runnable = new Runnable() {

        @Override

        public void run() {

            createNotification();

            Log.i(TAG, "updated");

            handler.postDelayed(runnable,1000);

        }

    };



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);



        ToggleButton toggle = (ToggleButton) findViewById(R.id.toggleButton);

        toggle.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {

            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {

                if (isChecked) {

                    // The toggle is enabled

                    createNotification();

                } else {

                    // The toggle is disabled

                    NotificationManager NM = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

                    NM.cancelAll();

                }

            }

        });

    }





}