FragmentTransacion with Fragment Activity

I'm using the NavigationDrawer to display the page options, I've adapted one of them to FragmentActivity to call some functions to work. But when I declare the transaction of the screens, it does not allow this, only with the Fragment without the activity together. This does not work FragmentTransaction.

FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction =  fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, mFeedFragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();