It could very likely be an infection, or, since he's putting no weight on it at all, it could be broken. Either would account for
swelling. I don't actually believe that bee
reaction is the most likely diagnosis for this (it wouldn't just swell like that, you'd be seeing respiratory distress, welts and/or the cat would be licking or biting at the site of the sting), but I can't tell more without details.
I really think that you should take kitty to the vet ASAP, ok?