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.
So sorry to hear about your diagnosis .
My Joshua was diag, with Lymphoma also. He's gone now but lived for
another 1 1/2 and died at age 16 years and 8 months.
I maintained him on multiple supplements and he was healthy up to the
last day he passed.
I use Only Naturals, Natural Defense Spray. It's made with Neem Oil and I've been using it for a number of years.
I ran out for a while this year and my Diva paid the price with a nasty bite from a spider.
She ran a 104.5 temp and her face blew up,she was covered in a deep red rash.
A visit to the vet for a shot of Dex and was on pred. for 10 days.
I made sure I had ordered the spray as it works for all kinds of creepy ,crawlies.
Kathryn and Diva Service Dog