As my cat is growing up, she is becoming so lazy. She just eats and sleeps. She does not even play with her toys anymore. She is 3 year old. Please help me. What should I do to make her active?
It's perfectly normal for cats to lose their playfulness as they age. Human adults don't spend their afternoon running in the garden the same way a child does either.
While there can be medical/ulterior reasons for a cat's behavior to change, including playfulness; your question doesn't give me any reason to assume that this is the case. 3 years sounds about the right age to no longer be playful the way a kitten is.
If the change in behavior was incredibly sudden, you can take her to a vet to make sure.
Other than that, try to provide toys and playtimes that you know she used to like (or buy new ones - depends on the cat's personality), but in the end it's the cat's choice whether she still wants to play or not.
Cats are most active in the company of other cats where they can play with one another. The most common form of play that even adult cats like is playful biting and playful wrestling using paws.
Even my cat is 1.5 years old and no longer is as active as she used to be while kitten. Only playful biting and playful wrestling stimulates her to become active.
Since I have no second cat, I myself play with her. I myself wrestle with her with gentle force so that she doesn't get hurt.
Also I keep her claws trimmed so that I don't end up having scratches. She never bites me hard. She bites me lightly in a playful manner so that I never get bruises.
I this way we can keep on playing for half an hour continuously at times.
Also she gets quite a bit of stimulation on seeing bird feather. The toys, where there is a wand with a string at one end and a bird feather tied to the other end, are her favorite.
Also her her favorite pasttime is sitting by the window side and watching birds.
You can try all these.
Also there must be other things which your cat liked as a kitten. You can try those or innovate new techniques on your own as well.
It's a bit like trial and error.