I have a small pea size hard rubberish lump behind my right ear (only one side). Around the location of mastoid process. It s neither painful nor movable. google said it s might be a common infection of lymph node due to a cold or flu infection. But I didn t have any cold or flu for the past month. I didn t experience any cold sweat, appetite loss, sudden weight loss (though it would be nice if that happen). No headache, vision or loss of balance either. I do feel very tired for no reason lately though. So is this just a common infection that will subside eventually or beginning stage of some kind of tumor/cyst?