Spot on my left bum cheek with a yellow head on it

Patient: I am a 24 yr old woman who has a spot on her left bum cheek, when my mum took a look at it, she said it has a yellow head to it, so i am wondering what it is and how to get rid of it? I am using savlon at the moment as i have only just found it this morning, and i dont usually get these kind of spot on my bum before. Please help