Hi. Thanks for your query. Noted the history and understood your concerns. The commonest reason for such a swelling behind ear is an enlarged lymph node. The others ones are cyst. This can be confirmed by the following: Clinical evaluation by a Doctor. Ultrasound and fnac if required. Once diagnosed, the treatment will depend upon the cause thus found. If cyst is found, get this operated. If lymph node, get a course of an antibiotic and anti-inflammatory medication. Watch for the primary cause like dandruff, ear infection and get an appropriate management.