A. This is probably due to a severe allergy, although it could also be fleas or mites.
First of all, in order to rule out skin parasites, you will need to treat him with a high quality flea treatment (e.g. advocate or advantage), then get imr to the vet to perform a skin scrape - this might revile an infection or a mite infestation.
If all of those came back negative, the next step is to treat the allergy symptomatically and try discovering the cause of the allergy.
Some medications can be given by the vet in order to stop the chewing and repair the skin lesions (steroids and antibiotics). simultaneously you should start him on a prescription hypoallergenic diet for at least 2 months.
Hopefully you will see some results after all this, if not you and your vet should consider putting him on a long term allergy treatment (Atopica or Apoquel).
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