A. It might be a stung again, especially if he is one of those who like biting on insects. It could also be an allergic reaction to a plant outside.
If it only look swollen but the cat is active and eating well, you can try half a tab (25mg tab) of benadryl twice a day and see if it helps.
Benadryl has a very bad taste to it needs not to be crushed but given directly to the back of the mouth with your fingers or a pill applier.
If he doesn't seem well take him to the vet as it could still be serious or even an abscess.
Your account has been reactivated.