It sounds like he gets hot spots which usually are the result of an allergy which is frequently a flea allergy. A dog with a flea allergy needs only to be bitten once to start the reaction going which leads to intense itching and even the development of lesions. Usually trimming the hair back, disinfecting with an antibacterial soap and hydrogen peroxide along with an antibiotic cream or witch hazel will help clear up any lesions or raw skin that occur. Unfortunately, if it is caused by a flea allergy, then even one flea jumping on him when he is outside can have an effect on him. Now you can use
Diatomaceous earth, which helps kill them in the yard without poisons. This can also be used in carpets as well. You can read more about that here.
Fleas do not like a wet environment so frequent watering of the lawn can also make it inhospitable to fleas as well. Of course, it would help to know definitely that this was the cause of the itching since any allergy could cause the reaction. Anti-inflammatory medications do tend to help worth allergy conditions, so It is understandable that the shots help. As you have seen though, steroids can have an affect on the personality as well.
I would recommend having allergy testing done so you know exactly what the dog is allergic to. Many dogs are allergic to multiple things and some to food items. Foods such as beef and Chicken are sometimes the cause. Most allergy diets are made of protein sources that dogs are likely not to have been fed before such as fish or venison and potatoes in place of other starches and fillers.
He is a relatively young dog and rather than continuing to spend lots of money treating the symptoms with antibiotics, shampoos, prednisone shots and special diets, it would be better to spend it on testing to see what the allergen actually is. Once the allergen(s) are known, they can then be avoided or if it is impossible to avoid, desensitizing shots can be given to lessen the reactions to the allergen and allow the dog to live a more normal life without the constant skin issues.
I'm going to give you some links on allergies and allergy testing for you to read over and discuss with your vet.
Here is a site that goes over itching in dogs.
I'm also going to include a link that lists various skin conditions for you to look over. Look over these as well and discuss the more likely ones with your vet.
I hope this information is helpful to you.