I understand that your fellow has had a non-itchy rash with fur loss on the side of his head for a while.
If this were itchy I would think of a contact allergy or an allergic reaction to an insect or spider bite or sting or a superficial bacterial skin infection.
But if it isn't itchy the most common cause of a rash with fur loss on the head of a young dog is a demodex mite infection.
All dogs have demodex mites in their hair follicles but in dogs with a suppressed, immature, or weakened immune system (such as young dogs, very old dogs, or a dog with a chronic illness), the mites overpopulate leading to fur loss and a rash. The rash isn't itchy, although it may become so if a secondary bacterial infection sets in.
This is diagnosed with a skin scraping at his veterinarian. Many times in very young puppies with only one area affected we give them time and see if their immune system will mature and handle the overpopulation without any treatment. But because his lesion has persisted and he is a bit old for this I would probably treat it.
He should be seen by his veterinarian for an examination and skin scraping.
In the meantime you can use a follicle flushing shampoo (Pyoben is one) only on the affected area every other day. Lather the affected area, let it sit for 5-10 minutes then rinse well. No need to bathe the entire dog. That spot treatment may help.
Other possibilities are a fungal infection (ringworm) or a bacterial skin infection.
Please let me know if you have any further questions.