Our cat has had exactly the same problem. I took her to the vet and was told it looks like an allergy to something.  The cat also had ear mites.  She was given drops for the mites and prescribed antibiotics for a week along with Diprogenta cream (anti inflammatory) to rub on her scabs.  Now, almost two weeks later she is no longer scratching as much and her scabs seem to be healing slowly.  Apparently cats are very complicated creatures according to the vet and to find out exactly what is causing the allergy would mean a lot of visits and tests.  Hopefully the problem will sort itself out.