Hi Aretha Stephenson,
Dogs that continuously chew may have a flea allergy or a seasonal allergy. For a flea allergy, the dog does not have to have many fleas, on bite is all it takes for an allergic reaction.
A seasonal allergy often shows up in the licking of the feet and chewing until raw.
Fungal infections and bacterial infections would also cause this , but the vet would need to take a skin scraping to determine this.
Hot spots (moist dermatitis ) is another reason for chewing.
You can give the dog benadryl to help with the itch. Make sure it is benadryl allergy and not the allergy/sinus. I would suggest since you are using flea control that the dog go in for a skin scraping to determine the cause.