Why is my 3 month old kitten sleeping all day?

Kittens, especially young ones like your 3-month-old, need a lot of sleep to grow and develop properly. It's normal for them to sleep for up to 20 hours a day. If your kitten is eating, playing, and using the litter box normally when awake, there's likely no cause for concern. However, if you notice any other changes in behavior or health, it's best to consult a veterinarian.