I am sorry to hear that your fellow is miserably itchy even with using antibiotics for his folliculitis.
You can use a combination of antihistamines and high doses of omega-3 fatty acids to help relieve his itch. In combination fatty acids and antihistamines work synergistically, much better than either one alone.
You can try:
1) Benadryl (diphenhydramine only don't use the combination products with acetaminophen or decongestants as they can be toxic for dogs) at 2mg to 4mg per kilogram of body weight or one 25mg capsule per 7 to 12 kilos of body weight orally every 8 hours. That would be two 25mg tabs for a 30 kilo dog every 8 hours.
OR 2)Claritin (loratidine) at 5mg per 11 kilos of body weight once or twice daily. That would be 15mgs per 30 kilos of body weight once or twice daily.
OR 3)Hydroxyzine at 2mg per pound of body weight orally every 8 hours.
OR 4) Chlorpheniramine (Piriton) at 4mg to 8mg per dog once or twice daily.
OR 5) Zyrtec (Cetirizine hydrochloride) at 1mg per kilo of body weight orally every 24 hours. That would be one 10mg tablet per 10 kilos of body weight. That would be 30mgs per 30 kilo dog every 24 hours. Make sure it is NOT the formulation with a decongestant (such as Zyrtec-D) because dogs cannot tolerate decongestants.
Some dogs do better on one antihistamine rather than another. Give the one you pick a week trial and if it isn't working try another. Be aware 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 40mg of EPA per pound of body weight per day. For example a 30 kilo dog could take 1200mg of EPA per day.
Cool water baths with an oatmeal shampoo or chlorhexiderm shampoo (which is antibacterial and antifungal) and a conditioner with an antihistamine may help. The water rinses off allergens and the cool temperature soothes itchy skin. Do not bathe your fellow for 2 to 3 days before or after applying flea control products or the bath will interfere with the product's efficacy.
Best of luck with your pup, please let me know if you have any further questions.