My dog does the same.Last years she had bald patches all over her body. The vet tested her for mites, mange, fleas you name it,but, he found nothing. Over the winter I thought she was growing out of it but, june hit and so did her time to go in season and she is biting lumps off her fur off again. the vet saws its in her head but, i don't like to see her so distressed. Advice given suggests having her dressed to kill hormones.Am doing so this weekend. will keep you posted.