It is my pleasure to "meet" you!
Bless you for rescuing Paulie and giving hm a wonderful home. You are AWESOME!
In my experience, cats that shake their head either have itching or discomfort in their ears, a bad tooth, mucus in ther nose or an issue with their mouth.
The ears, nose and mouth are intimately related so check roof, under tongue, cheek pouches and between lips and teeth.
Ear mites live deep inside the ear. You cannot see them with the naked eye.
read more here:
Since that medication you used is very messy and can even sting, I would just apply monthly revolution to Paulie. It kills fleas, ticks, ear ites, some worms and even affords some heart worm protection.
If you think he has an upper respiratory infection he can have benedryl @ one mg per lb every 1 2 hours.
If he has an ear infection deep inside the ear he may need vet scripted medication
Please let me know how Paulie is doing.
If you still have questions, just press reply and I will be here for you.
Warmest best wishes,