It looks like your buddy is suffering with a skin problem called Atopy or Atopic dermatitis. I assume he has not got parasites if he has been seen at the vets. But always think of this first.
If you have no fleas or mites present then allergies or food intolerances are likely. First and most important get him on a real food diet, preferably raw foods but certainly NOT kibble or other ultra processed food. Try to find something he is not used to eating something fresh. This can make all the difference. Look in the nutrition section for more info
Herbal mediciones - first use Cessorex https://naturalpetcare.co.uk/shop/cessorex/ which can help so many itchy dogs. But also shampoo or bathe in a mild shampoo Aloe & Oatmeal perhaps or bathe in Chamomile tea (cold), give extra oils in the Diet Proflax Skin and coat is great https://amzn.to/3QQiJ0B for this but many oils will help. Probiotics are also very helpful. Nutraflora, Pet Plus kefirs all help. The skin microbiome is ouit of kilter.
If that helps then give different food one at a time ab out 2 weeks apart to see if you can work out what he is intolerant too.