I'm A 28 Year Old Female And Have A Small

I'm a 28 year old female and have a small dent in the center of my forehead right below the hair line. I have had it for about a year now but it seems to be getting worse. It's hard to miss it now, that's all I see when I look in the mirror. It looks as if I took my index finger and pushed a small indentation into the top of my forehead. I haven't had any recent head trauma. Can anyone tell me what is causing this? Why it's getting worse and how I might be able to prevent that from happening?
Thanks!