It sounds like he is affected by allergies which is very, very common on hot, humid days, either indoors or outdoor dogs.
I would recommend bathing him in oatmeal based shampoo with itch relief that you can pick up at any pet store. Make sure you leave it on for approximately 10 min so the soothing affect can absorb and work faster. Bathing every other day until the areas are healing and drying up is very beneficial then bathing once a week until they are cleared up and itching stopped.
Benedryl is great to use not only to help the itching and inflammation but it also helps calm your baby so he is not wanting to chew all the time. Benedryl dose is 1 mg/per 1 lb. One adult benedryl is 25mg so if he is 25lbs, give one up to three times a day. This can get the itching under control then back off as needed.
Any hydrocortisone spray can help on the areas as needed especially since you have an e-collar and you can use the sprays in between baths. The kind that you are using may work. I would not use the vitamin E on there cause this can trap the moisture and not allow it to breath to heal. You want it to dry out but control the itching while it is drying out.
Bathing is the key to hot spots and if not controlled, more will show up in form of a lump then into rash, then its a continual cycle. Allowing it to dry out will help so nothing topical unless it is the anti itch spray. One that you have is fine just make sure it has hydrocortisone in it. No other oils need to be applied. Benedryl will help dry it out and prevent itching and control inflammation. So try regular over the counter straight benedryl with no additives. The calming tablets will help just calm your baby but benedryl has beneficial factors that help calm your baby, the skin, and drys it out.
It would not hurt to keep your appointment at your vet. More than likely they will give a Cortisone shot, or give you oral steroids which will be a quick fix and save you the trouble of fighting this on your own.
Please feel free to let me know if I can help you any further.
(Patience is the key & hopefully all you guys can get some rest soon)