A couple of days ago I was running my hands through my hair to discover a lump at the back of my head, perhaps an inch into my hairline from the base of my neck. It's hard and only hurts a little if I apply pressure to it. It's located more to the right side of my head and is about the size of a dime. Can anyone help me? I plan to make an appointment with a doctor as soon as possible, but at the same time I'd like to have some theories on what it might be, if only to ease my own anxieties.