My New Name

I try and try to teach Aiden to say "MAMA." He won't, he refuses instead he calls me "Nana." He never babbles it.  He uses it correctly 100% of the time. When he is on the floor and wants to be picked up he screams Nana, when I turn my back and he's in his highchair he says Nana and when he's done nursing he says Nana. I don't know if this is normal but I'll take it!