What Causes Pain And Bump On The Back Of The Head?

I've noticed every now and then the back of my head feels sore, like i hit it. When i go to touch the soar area there is a small bump. After about a day or two, it goes away. I've noticed that when this does occur its usually around a time when I've had alittle too much to drink. Do you think this is related to alcohol? I have had two falls to back of the head over the course of my life, nothing that took me to the hospital, but definately accidents that left a goose bump there for awhile. Do you think there's connection to that also?