How old is he? What does he eat? I suppose he isnt longer with mom, you did adopted / bough him?
How is he doing otherwise? Playing etc?
A common reason cats do poop very much is they get to eat dry cat food with much cereal contents. Them cereals in cat food is mainly a fill up - thus: much poo.
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ps. I had asked a mod to make a your own tread of this post by you. This way, it will be more visible and will get more answers.