If the doctors who examined you and performed an inconclusive biopsy are stumped, I'm afraid I can't be definitive either. Over the years I have seen patients who have intermittent itchy, sensitive swellings that sound somewhat like what you're describing. Sometimes I've had to treat them with short courses of oral steroids, to shorten the course and mitigate the symptoms. Of course, it's better to know the cause, but in such cases there may be no specific discernible cause, which leaves symptomatic treatment the best available course. You might talk this over further with your doctors.
Best.
Dr. Rockoff