What Causes A Lump Behind The Ear?

hello. i am a 20 year old Male. i have a nickel sized lump behind my Letf) ear. and had it since i was 13. i got up one morning and it was just there?. anyhow i now am starting to get my wisdom teeth in. No bottoms just the Right Top one is almost fully in. it Doesn t hurt but reciently the lump behind my (Left) ear is starting to hurt And i wonder if this could be cause d from the wisdom tooth? i went to the clinic a few months ago for the tooth And the Doctor said. she required a dentist for the tooth problem. she looked inn my ear and said everything looks normal. i have had swollen glands in the past. and i had her look at thoes also. she replied they Look normal!! iam fairly scard about this situation and dont know what to do? PLEASE ANY HELP WILL BE WONDERFULL AND CINCEARLY THANKFULL -paul