Hello and hope you are doing well.
It could be enlarged lymph node/nodes. Lymph are protective mechanisms of the body and they 'trap' the infecting source causing enlargement of lymph nodes. The infection can be from the draining skin or the organs. The other causes for enlarged nodes are tumors or inflammations to name a few. The swelling could also be due to mastoiditis, which is infection of the bone behind the ear. This happens when there is a middle ear infection, which spreads to involve the mastoid bone. If the swelling does not resolve with antibiotics, a biopsy may be indicated. Discuss these options with your doctor when you happen to meet him next time.
Hope this helped and do keep us posted.