I'm sorry to hear about your boy - pugs are such wonderful little dogs. One of my boys, Piggy, is a pug!
I think it's very possible that your little guy is experiencing an allergy. The problem is, we don't know precisely what's causing this allergy. It could very well be his food, but it could also be something else in his environment, such as a chemical (i.e. the laundry detergent you use).
With his chin, there could be a couple of things going on. These bumps could be the result of the allergy, or they could be pimples. Pugs especially are prone to acne and this is a common spot to see this. Acne can also result from allergies, so I think that this is a likely scenario.
To help with his chin, I would get a mild wash containing benzoyl peroxide. There are dog formulas out there, but a mild human formula designed for sensitive skin can work too. You can wash the area with this once a day, preferably after breakfast. In the evenings after he eats, you can use antibacterial soap to wash the area. Clean with betadine (available in the first aid section, near the hydrogen peroxide) and then dab some antibiotic CREAM (not ointment, as this can clog pores) on any areas of broken skin.
Another possibility could be some sort of infection with his chin -like a yeast infection. You'll usually see small red bumps, dryness and a roughness to the skin's surface, oozing and intense itching. This can also be spread to the legs and feet, so that may be something to explore as well.
I would also review his food bowl situation. Plastic bowls get microscopic scratches that harbor bacteria and it's transferred to his face while eating. So no plastic bowls - stick with ceramic or metal. You'll also want to wash them thoroughly after each meal.
As for his food, you may want to try a dog food formula with duck and potato or lamb and rice, as these are commonly tolerated formulas among pets with food allergies. I personally like science diet foods over Nutro, but if he's allergic to a component that's contained in both, then it's just going to harm him. I know pro-plan makes a lamb and rice formula that's widely available. If you're willing to spend the money,
Pinnacle Duck and Potato is my top recommendation for a dog with allergies. It's a bit hard to find, so you may have to order online. Here's a site where I've bought it:
Licking and biting at the feet and legs is a classic symptom of allergies, so I think that once you get the situation under control, you'll see this disappear.
One option would be to try your boy on some Benadryl and see how he reacts (providing she's on no other meds. If she is, check with your vet first). I prefer the dye-free children's liquid Benadryl. For a dosage, you can give 1 mg per 1 pound of body weight, given every eight hours (three times a day). If you decide to use the pills, you can stick them in peanut butter or cream cheese - I've found that this is the easiest way to get our pets to take pills! And if the dog responds well to the Benadryl, and he improves, then you'll know for sure you've got an allergy to blame. If he doesn't respond, it's still possible he could be dealing with an allergy, as some can be very stubborn. You can certainly speak with your vet, who can try him on a prescription n anti-histimine as well.
Here's more on food allergies:
Don't hesitate to let me know if you have any additional questions! And I wish you good luck with your pug - I hope he's feeling better soon!
***Please ACCEPT if my answer was helpful!****