The left side of my 4 year old Staffy's jaw is swollen. It is a little warm and hard, and the skin under his jaw is saggy. He does not seem to be in pain, and is otherwise acting normally. I have given him 25 mg of benadryl, which has not reduced the swelling (now 3 hours later). I managed to get him to open his mouth, and there was no obvious mouth/tooth trauma (but it was a very brief look). He did grab a dead fish while we were walking yesterday, but dropped it pretty quick when I made it obvious that that was not an appropriate toy. I don't think it is an allergic reaction or a bee sting/bug bite. Is there any way to know for sure? Any other things it could be?