It is more than likely mastoiditis which is a bacteria infection of the air cells in the mastoid bone of the skull. The actual areas are called mastoids they are generally caused by an infection of the middle ear called the otis media.
Treatment if needed is antibiotics, not for the mastoids but for the middle ear infection. If your new mastoid just came up you probably need to go to the doctor to see if you need antibiotics or not.
hi ther i get this too. think its just blocked glands,i have one on the back of my neck and have got one behind my ear also. does anything come out of them if you squeeze or have they ever gotten sore to touch? just wondering because mine does.
if your very worried maybe a trip to the doctor would sort it out for you.