Dog Allergies Treatment

My dog, Winter, scratches all the time. He doesn’t have fleas. I believe he may be getting bit by ants or he may have skin allergies. I hate seeing him like this. And recently it’s getting worse. Unfortunately, the vet can’t see him until next week. Can you answer these questions for me?
What is the proper dog food to by for dogs with itchy skin?
What is the proper shampoo for dogs with itchy skin?
How often should I bathe him?
-I was doing once every two weeks is that too much or too less?
What else should I be doing until his appointment?

My 1.5 year old lab has red sore spots that turn into scabs on his belly. He has had them for a while, but they never seemed serious or a problem. He had skin issues about a year ago when he was just a puppy. I put him on premium food and it went away, but he has always been a bit itchy I believe, and it is not fleas. I’m wondering if it’s allergies or if it’s serious that I need to go to the vet. Last time I took him to the vet she acted like I was stupid because I brought him in because he was itching a lot. She had asked me if I ever owned a dog, which I have when living with my parents. I’m a 21 year old college student and this is my first dog that is mine and I make all the decisions for. So I want to know if this is serious enough to go to the vet.

This cat is allergic to fleas, so we make sure to keep that problem resolved. We have taken her to the vet and she has no fleas (he did give her an allergy shot to be sure), she does not have mites, neither does she have infection. He did an allergy test on her and found nothing other than the allergy to fleas. Even though she was only scratching her ear, I had the vet check everything from mites to worms, just to be on the safe side.
In the past, once I saw her scratch even once, I would use her flea med immediately and the problem would be solved. I rescue animals so sometimes one will bring a flea in, even though I quarantine the new ones, stuff happens sometimes. And I stay prepared. I also have the exterminator come every three months … an ounce of prevention.
She began scratching about three weeks ago and I began the ritual. However, when I checked, I saw no sign of fleas. Now I do know when a cat or dog is allergic, one can wreak havoc – and there is never just one.
When she did not stop scratching after the first day, I loaded up the kitty carrier and took her to the vet. I have done this three times and he has not found anything. She has scratched until the spot just behind her ear is raw, and it looks terrible. I have a natural medication I use on it and that is about the only thing that helps. I have tried all of the medications and they make her ear burn, cause her obvious pain and do little to even help the raw area. My problem is, even after I put the natural concoction on that helps, she will wait a day and then begin scratching again. Thus, about time it scabs over and looks like it might heal, she breaks it open again. I just put the medication on her rear again this morning and she actually purred while i was putting it on, and then began rubbing against my legs as cats will do when they are happy. I sat and held her for awhile so she would not try and rub the salve I made off, and the little booger actually took her paws and wrapped around my neck as if she were hugging me.
I am just totally stumped! I have never seen any animal keep scratching as she does, even when I know it is hurting her. I am worried she is going to permanently damage herself.
Any thoughts, ideas, or suggestions?
Add: We have tried the basic anti-itch medications as well.

I thought she had a thyroid problem but it doesn’t look like that is the issue either. And she doesn’t have fleas.
I am stumped and she is miserable.
Help!

i use frontline and i haven’t noticed any fleas so is there a good brand that will help with possible dry or allergy prone skin? i’ve been to the vet several times and they are no help cause they don’t know why she’s itching.