onPageSelected doesn’t work for first page

You can manually call onPageSelected(0) when you create your OnPageChangeListener to set the starting state:

OnPageChangeListener pageChangeListener = new OnPageChangeListener() {
    @Override
    public void onPageScrollStateChanged(int arg0) { }

    @Override
    public void onPageScrolled(int arg0, float arg1, int arg2) { }

    @Override
    public void onPageSelected(int position) {

        switch (position) {
        case 0: 
            QuizStart.next.setText(getmycurrentpage()+"");
            break;

        default:

            QuizStart.next.setText(getmycurrentpage()+"");
            break;
        }
    }
});

   mPager.setOnPageChangeListener(pageChangeListener);
   // do this in a runnable to make sure the viewPager's views are already instantiated before triggering the onPageSelected call
   mPager.post(new Runnable()
   {
       @Override
       public void run() 
       {
           pageChangeListener .onPageSelected(viewPager.getCurrentItem());
       }
   });

Edit

Now it will not get Null Pointer exception as pointed by @metemet06