Hello, my name isXXXXX and I have over 20 years of experience as a veterinarian.
I'm sorry to hear that your pup Alfie has had itching and hair loss along his backline. This sounds like a secondary skin infestion from him biting and chewing on himself because he is so itchy, allowing bacteria that normally live on the skin to get in the skin and thrive.
Getting him to stop licking, giving oral antibiotics and allowing the skin to heal helps, but of course if we don't treat the primary reason for his itch then it will return.
Allergies are the most common cause of itchy skin. I'll give you an allergy rundown of likely causes for skin troubles. He may have more than one allergy given how symptomatic he has been. Dogs that have one allergy often develop several with time. The effect of multiple allergies aren't additive, they actually compound one another.
Even if you don't see fleas I do recommend using protection. They are the most common allergen and the backline is the most commonly affected area. It only takes one bite a month to make an allergic dog scratch so I recommend using flea prevention even if you never see one again. Frontline Plus , Advantage II or Advantix are excellent. Don't use over the counter products, especially Hartz or Sargents, as most are ineffective if not toxic.
Other allergens can be inhaled (like grass pollen, dust mites or molds) and you can use a combination of antihistamines and high doses of omega-3 fatty acids to help control his reaction to those (they also help with the symptoms of flea allergy). In combination fatty acids and antihistamines work synergistically, much better than either one alone. If his symptoms worsen seasonally I would think that inhaled allergens are a part of his problem. Don't worry about keeping him on antihistamines too long, they are quite safe and can be used long term if need be. With seasonal allergies I have owners start antihistamines 2 weeks before the season and continue through the season. But some dogs need them year round.
You can try:
1) Benadryl (diphenhydramine only don't use the combination products with acetaminophen or decongestants as they can be toxic to dogs) at 0.5mg to 1mg per kilogram of body weight or one 25mg capsule per 12 kilos of body weight orally every 8 hours.
OR 2)Claritin (loratidine) at 5mg per 12 kilos once or twice daily.
OR 3)Hydroxyzine at 0.5mg per kilogram of body weight orally every 8 hours.
OR 4) Chlorpheniramine at 4mg to 8mg per dog once or twice daily.
Some dogs do better on one antihistamine rather than another.
Give the one you pick a 5 to 7 day trial and if it isn't working try another. Be aware that antihistamines can cause sleepiness or hyperactivity in some dogs. These side effects do wear off with repeated use.
Omega-3 fatty acids are fish oil products. 3V by DVM or Derm Caps ES are good brand name products. Use the high end of the dosing schedule for your pup's weight.
I recommend a dose based upon the EPA portion (eicosapentanoic acid) of the supplement as if we do that the rest of the supplement will be properly balanced. Give him 20mg to 40mg of EPA per kilo of body weight per day. For example an 8 kilo dog could take 160mg to 320mg of EPA per day.
In some cases the pups may need oral antibiotics too here and there if they itch enough to cause lesions.
Another option if the antihistamines and omega 3's aren't enough is a product called Atopica. It suppresses the immune system a bit so it decreases allergic symptoms but it doesn't have as many harmful side effects as systemic steroids. Another option is a brand new drug called Apoquel (generic name oclacitinib) which interferes with the allergic pathway. It works very quickly to stop the symptoms of an allergy. Most dogs are reported to be much more comfortable in a day or so. If you are interested discuss these medications with your veterinarian as they are prescription products.
Please let me know if you have any further questions.