Buttons is putting weight on and I can't understand why. She is the smallest of my four cats, eats the same as they do, and plays as much as they do. She has been getting quite tubby over the last two or three weeks and I can't fathom out what the problem is. She is waddling, and her legs are too little to support her weight. I am taking her to the vet on Monday and I am really concerned. Has anyone suggestion as to what it may be?