What Causes A Lump Behind The Ear?

hi i noticed this morning a hump behind my ear, not very close to the ear,almost in th middle of the head...it hurts if i press it and i am pretty sure i did not hurt myself anywhere on the back of my head.it is very close to the spot the glasses end behind the ear, a little bit further to the middle of the head..what is it? should i go to a doctor or wait..i hope it's not canser :(