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Hello. Thanks for the question.
This may be a flea allergy dermatitis causing these issues. Flea allergies can lead to fevers, skin lesions and discomfort. The discomfort can cause the panting you're seeing. It may also be a fever and some type of infectious or auto-immune condition. If you can check a rectal temperature, that would help. Normal is 100-102. If > 103, then that could explain some of the issues.
If you want to try some Benadryl to see if that helps, you may get some relief for him. The dose in dogs is 1-2 mg per lb body weight. It can be given every 6-8 hours, as needed.
Here is a nice link on combating flea infestations to read over with more info on how to help: