Hello, I have a lump on my left bum. Its not spot or anything. There is a small lump/hill and still has skin over it. its sore when i sit most times and i had this for about a year or two. I remember when i was out sailing i sat down on something hard really fast and from then it started to form this lump on my bum and thought nothing of it until now and want to know if it is serious. Im 17 years old if that matters.