i agree with the others a trip to the vets is a must for poor kitty. the smell is usually a sign of infection so good you noticed it cause if kitty is a fighter it wont be the last time you will smell it, possibly is an abcess my tom has had a few of them it will involve a antibiotic jab and maybe some pills, if you have problems getting the pills down kitty then a deli chicken from tesco usually sorts any problems out, just tear off a bit of chicken and wrap the pill in it. works for my tom every time no stress at all.