loosing weight very quick

my cat is aprox. 6-7 years old about 2 months ago she was fat and healthy within a months time she lost allot of weght all the way to just skin and bones she also is not cleaning her nails any more and getting week. she is still very lovable though.
   
i checked her poop for worms and nothing, we changed her diet about eight months ago we also have two other still healthy cats

You need to get to a vet for a blood panel. It could be hypertyroidism or kidney or liver problem. You should go soon before the problem is iriversable. Good luck!

Is she having trouble eating? or a lot of saliva coming out of her mouth?
   
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