A few guesses….
While you were pregnant you started sleeping with your mouth open and you still do. That’ll give you crazy dry mouth.
Or.. babies suck your life force right out of you and steal your liquid essence. And you need more fluids.
Or.. food contains water and in taking in less food you are also taking in less water. So drink more water.
Keep in mind I’m a legitimate idiot, so it’s also possibly none of these.