I'm having to clean my cat's litter box more and more these days, why is that ?

My cat is 12 years old, his name is Fred. We used to clean his litter box maybe three-four times a week. Now i'm cleaning two, even three times a day. It's clumping more than it used to, and these clumps are huge. Proably the size of my head. It's never been like this before, and i'm wondering if... show more My cat is 12 years old, his name is Fred. We used to clean his litter box maybe three-four times a week. Now i'm cleaning two, even three times a day. It's clumping more than it used to, and these clumps are huge. Proably the size of my head. It's never been like this before, and i'm wondering if maybe it's because he's peeing more often. Maybe his kidneys are having problems because of his old age. I have no idea, i'm lost, please help.
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