I Am A Teenager, I Was Told That I Was

I am a teenager, I was told that I was never dropped as a baby or child, also I've never had any big accidents that included my head or any area near my face. I have an indent on the back of my head, it is very fragile, soft and if pressure is put on it hurts. Any ideas why its there? My name is Elizabeth, Thank you very much, hope to get back to you soon.