Is the swelling red and does it hurt and also is it increasing in size?
It could be mastoiditis. Mastoiditis is a infection in the air pockets of the mastoid bone. It presents as a painful red swelling. Another cause could be an enlarged lymph node or a vein. It could also be due to an ear infection. I would suggest you to schedule an appointment with an ENT specialist as soon as possible.
Thanks for your reply. The lump was never red but it was pain when first discovered a month ago. It was slightly raised but grew bigger to a size of a small marble. Will take your advice to schedule him to an appointment with an ENT specialist. However, could it be any other causes besides the ones you mentioned. Please let me have your reply. Thank you.