Is the sound of its voice all we have to go on? I only have one, so I do not know how to compare the loudness of the quack. I've heard much louder quacking at the lake from the ducks that want your bread scraps...
You should, at least, hear a raspy-sounding peep or squeak by now if it's a boy. Girl peeps at that age are usually louder and sometimes you will hear a quack now and then at that age.