Is the vet sure it was an ant bite? There was another thread here, where a Yorkie got a foxtail and the vet didn't find it at first, they are very small.
Quote:
The mature seeds that detach from the plant are barbed like a fish hook. They are very sharp, and are easily picked up in the fur, ears, and paws of dogs. Because of their structure, they can work their way into the skin, causing infection and may even translocate to the organs.
How can I tell if my dog has a foxtail?
A dog that has a foxtail stuck will often attempt to remove it, depending on its location. If it’s in the dog’s nose, it will repeatedly sneeze or paw at its nose. If the seed is in the eye, the eye will water or even be swollen shut. Foxtails lodged in the skin or paw will form a painful, pus-filled lump. Foxtails And Dogs | Healthy Paws Pet Insurance & Foundation |
It's best to let your vet know how your dog is doing, and you could ask him about Benadryl spray, if you are sure it's an ant bite, but I can't believe an ant bite would be bothering him this long.