Here's an excerpt from the following website...
Healthy Dogs - What can poison your dog? Due to the significant toxicity to pets in relatively minimal dosages, the recommendation is clear - Tylenol should not be given to dogs or cats. Other, safer, drugs are available for pain relief; talk to your veterinarian about your own pet's specific needs.
Tylenol is very dangerous to the liver and since this dog had such a negative reaction to shots, I would not take the risk...Basically everything is filtered through the liver and I would think this would be an overload on him. He just got his shots and had a bad reaction, and then tylenol...
Like Ellie May said, typically vets will recommend a very small amount of benadryl for a reaction like that. Maybe you could can call your vet for advice.