My 3 week old kitten just sleeps and drinks kitty milk. Is that normal?
It’s normal for young kittens to sleep a lot. Actually it’s normal for most cats to sleep a lot! As a ballpark, kittens can sleep anywhere between 15 to 20 hours per day (even more in really young kittens).
The one thing I do want to check on is the ‘kitty milk’ you’re using. Is she being exclusively fed from mum or is she being supplemented with a proper kitten milk formula? Kitty milk from the supermarket isn’t a balanced food for kittens. It has nothing on mum's milk and can cause major deficiencies when fed exclusively.
From around three weeks, it’s time to start introducing solid kitten food.
It’s also important to weigh your kitty every day to ensure there’s daily weight gain––it’s the best way to assess healthy growth. You also need to monitor that she can go to the toilet normally. (At this age, you or her mum still needs to help!)
If she hasn’t been gaining weight, is having trouble with the toilet or won’t eat her food, I’d recommended a hands-on examination from your local Vet as soon as possible.