licking , scratching & chewing

First of all, I can assure you that this is NOT pin worms. Worms of any kind, would not be the cause of this excessive scratching. The shot that your vet is probably wanting to give, is a steroid shot. This shot does not "fix" the problem. Instead, what it does, is "mask" or suppress the symptoms temporarily.

Does the possibility exist, that your dog might have one or two fleas? Fleabite allergy is extremely common. It could very well be the cuase of the excessive scratching. One flea bite could trigger this behavior.

I see no fleas and he is on Frontline, but it is time to apply again, perhaps it doesn't last as long as advertised.

Your dog may have a food allergy. Science diet foods including their skin and coat food is corn based and dogs are often allergic to corn.
Sensitive Skin Adult food from Hills has these ingredients
Brewers rice, corn meal, corn gluten meal, chicken by-product meal, dried egg product, vegetable oil, animal fat (preserved with mixed tocopherols and citric acid), flaxseed, chicken liver flavor, DL-methionine, L-lysine, L-tryptophan, preserved with mixed tocopherols and citric acid, minerals (potassium chloride, dicalcium phosphate, salt, calcium carbonate, ferrous sulfate, zinc oxide, copper sulfate, manganous oxide, calcium iodate, sodium selenite), rosemary extract, beta-carotene, vitamins (choline chloride, vitamin A supplement, vitamin D3 supplement, vitamin E supplement, L-ascorbyl-2-polyphosphate (a source of vitamin C), niacin, thiamine mononitrate, calcium pantothenate, pyridoxine hydrochloride, riboflavin, folic acid, biotin, vitamin B12 supplement).
Many dogs are allergic to corn and to eggs! and for some the mixed tocopherols used as a preservative can cause a problem.
You might do better to swap your dog to Evo or California Natural or Wellness Fish and Potato to see if that resolves the problem for you.
If its a food allergy it can take some time for a food change to show relief and you have to not give the dog 'treats' unless its the same formula as the food you are trying.
Hope this helps you!

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Thanks, I had considered it might be a food allergy.I will try changing his food to one you have suggested. It will be hard to forgo snacks, but would cheese and chicken strips cause a problem? He also gets "greenies" almost every evening, I will check the label on those too.
:) Char

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