There are alot of clinics out there that will look at your cat for free or very little money and let you pay out...I agree that the cat is more than likely in some kind of pain and needs to be looked at.
I sure hope that you have enough clavamox to last 10 days. I really believe that your cat has an abscess and has an infection. He probably got bitten in the leg by the other cat, which caused it. To be honest, if your cat is favoring one leg, then the other leg hurts him too much to walk on it. It's possible that your cat is in pain. I really hope that you have enough clavamox, your cat needs it!