What Causes Lump Behind The Ear?

Hello, I have a lump behind my ear and im very worried about it.. I had a MRI scan a few days ago cause i thought i had a tumor as the front of my head seems to extend out then sometimes it goes down, iv goggled about everything it somehow the word tumor seems to be involved. I m 18 and my name is kelsie... im am very scared... The MRI came back with showing nothing, but everything i good has tumor in it.. i dont know what to do... i don t want to die hah