Are you SURE it is an allergy .
When did your B have his last rabies shot ?
This happened to my Diva right after her rabies vaccination.
It took a full month before she was better.
Word of advice, stay away from rabies vaccine ,your B is 9,they are not needed.
Hope you live in a state that has exemptions.
Take a look at the website from Dogs Naturally called
65 Ways Rabies Vaccination Can Harm Your Dog.