First thing I would do is Vet him and probably agree to a short course of corticosteroid, like Vanactyl P, to stop the itch cycle. If he is scratching to the point of injury and limping his open wounds can allow serious infection. I will guess your Vet might try him on an antihistamine or both.
This summer in much of N. America has been very bad for those with seasonal allergies, human and dog. My dog started itching much soomer this year.
SEasonal allergy is a more common reason for itching than food, in many readings I've done. Google, you will see. Personally, if the food is working I would stay on it and attempt to change only one thing at a time. If you are lucky it is seasonal and will clear up when the weather cools. I am assuming it is a new thing. Then you could try a better food. My dog is on a three food rotation. He will itch on all three in the hot, humid weather, he is fine on all three in winter so it was easy for us to tell it was seasonal and not food.
Many, many dogs are smelly this summer, last summer too. The heat and humidity does it. Oatmeal baths were recommended to me too, haven't tried. 50/50 water/vinegar or a lesser amount of epsom salts/water may also help but do not get either on broken skin. The vinegar one will help with smell too, but for the itch I had to repeat often, like several wipedowns a day.
First step is your Vet.
How are his ears? My Vet says if ears are yeasty it can transfer to feet when they scratch. Too many possibilities to deal with on your own, I think. Vet. Good luck. Poor little guy.