The most common cause of these crazy skin problems IS allergies, especially with this breed. These allergies could be from grass, contact with a cleaner or chemical or could even be food related. The allergy part is sometimes tough to treat but there are some simple things that you can do.
When the dog abrades the skin by chewing and scratching, this opens up the body to infection. Many dogs need antibiotics because of this.
See the vet so that they can get the dog started on an antibiotic if you suspect this.
Many dogs also need a shot of prednisone to control the itch and give the skin time to heal.
Keep in mind that you thyroid conditions can also cause hair loss and skin issues so you will want to have this checked if the suggestions above do not help.
If you have done everything that I mention above, your next step is going to be allergy testing so that you can find out exactly what he's allergic to.
I hope this helps!
Let me know if you still have questions.