FragmentManager fragmentManager=getSupportFragmentManager();
 FragmentTransaction transaction= fragmentManager.beginTransaction();
 transaction.replace(R.id.container, fragmentB,tag).addToBackStack(null).commit();

@Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            FragmentManager manager = getSupportFragmentManager();
            int count = manager.getBackStackEntryCount();

            if(count==0) {
                super.onBackPressed();
            }else{
                manager.popBackStack();
            }
        }
    }

private View view;

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

        if(view==null)
          view = inflater.inflate(R.layout.article_view, container, false);

        return view;
    }