cause of frequent head shaking and ear scratching?

My cat Lexi shakes her head more than normal I'm sure. She also has scratched a raw spot under her left ear. She scratched that spot raw last June and the problem resolved without intervention. The head shaking continued some over the winter and then in May this year she scratched the spot raw again but worse. Same ear same place. Photo below was at its worst. It healed nicely in the past few weeks and hair filled in. But today she again broke open a small scab. Vet has inspected ears on several occasions and has never seen signs of ear mites or other issues. A month ago the vet said perhaps it's a seasonal allergy. Or else a food allergy. Per vet advice I apply Neosporin and hydrocortisone ointments as needed. Vet suggested we could try a restricted diet. I feed her Merrick chicken pate and turkey pate and Nature's Variety duck and rabbit. A wide variety of proteins. Next step after that, if needed, would be a skin test and/or blood test for allergies with a preference for the former. Said we'd need to travel to a specialist 2+ hours away. Lexi does not appear to be in distress but I'd like her to be 100% well and I'm not sure she is right now.

Would you wait and see or restrict diet?  Vet said a restricted diet is a real challenge these days given the way cat food is prepared. 

I would be more likely to try something for seasonal allergies - either cortisone, depo-medrol or zyrtec.  I have two on 1/4 tablet of Zyrtec daily for seasonal allergies and it helps a lot with the scratching.

Red Top Rescue said:

 
I would be more likely to try something for seasonal allergies - either cortisone, depo-medrol or zyrtec.  I have two on 1/4 tablet of Zyrtec daily for seasonal allergies and it helps a lot with the scratching.

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Interesting.

I should have mentioned that she goes outside a bit, and I have her on Frontline Plus (and Heartguard), and she's a few days overdue for another dose of Frontline. I'm stopping by the vet today for some. Will ask about the merits in trying the meds you suggest.

Update:

Lexi is still scratching. History.

June 2015, scratched a raw spot size of a dime below left ear. Resolved in a month.

May 2016, scratched below left ear. Photo in a above post. Resolved in a month.

July 2016, scratched a raw spot under right ear. Applied topical Neosporin and hydrocortisone. Resolved in a month.

September 2016, scratching nickel size raw spot on/under neck. Photo here.

A few months back my vet presented the option of a skin test for allergies by a specialist 2 hours away. Lexi does is not in obvious distress. Playful as ever. But I'm starting to get concerned that this will be a life-long quality of life issue.

I have had a cat with food allergies. I spent over a thousand dollars on  vet visits and medications.  I was so confused at the try this..try that..now try this.  I did get it fixed. I dont feed her any cheep foods. I dont feed her anything that she has had in the past. For me that was rabbit. ONLY rabbit.  She has been on that for 4 yrs now. It worked for me.

Good to hear of your success. My cat has been eating chicken, turkey, duck, rabbit, and lamb. We're soon starting a prescription elimination diet. Likely venison and potato. Have an appointment with a veterinary dermatologist in 5 weeks. Want to get this figured out soon. 

I wish you the best of luck.  And a quick fix!