Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your wee one’s situation, and wanted to help.
Again I do apologize that my colleagues could not aid you sooner, but can you tell me:
What dose of Benadryl were you giving? How often and what does he weigh?
Where is he scratching specifically?
Any changes to the skin (ie pimples, pustules, scabs, ulcers, sores, dander, or crusting)?
How often are you using the frontline plus?
What does he smell like (since you noted an odor)?
What medication did his vet try?