Why Do I Have A Vertical Indentation In My Forehead That Drops With Pain Sometimes?

Hello, I have a vertical indentation on my forehead I just noticed today. About 1.5 long on my forehead that goes down into my eyebrow. When I press on it, it feels indented and it s painful. Now that I ve pressed it a few times, it s throbbing on my forehead and behind my eye. Today is the first day I ve noticed it. Can someone please help me?