Hair Loss back of ears

Question
I have a 1 1.2 yr old spayed fawn female- started hair loss back of ears- almost down to skin- negative thryoid blood test. Not scratching. Have not changed food or no environmental changes. Vet perscribed antibiotic ointment for ears- not helping

Answer
This could be many things, but since you've seen the vet I'm guessing a lot of them have been ruled out (thyroid you mentioned, ear mites, skin mites are other possibilities that the vet most likely will have checked).  I tend to think - though this is not proven anywhere that I could find - that symmetrical hair loss behind the ears (or elbows), in the absence of any other symptoms (skin irritation, itching, thyroid issues, etc.), is hormonal/endocrine related, similar to seasonal flank alopecia that is not uncommon in Boxers.  You might try giving some melatonin, as advised for alopecia, and see if that helps.  (Of course whether melatonin actually helps, or whether the condition would have self-resolved in the same time frame, is debatable itself.)

Good luck!