Is an anal inflammation normal?

I'm a 17 year old female and randomly got a rather large inflammation on the outside of my anus. It's painful, especially when I walk, and I've had it for two days now. I have never gotten anything of the sort prior to this, and I do not and have not ever had anal sex. It's kind of hard and shaped oddly, it is not circular. I'm really scared because I have no idea what it is or what to do. Please help if you have any idea as to what it could be and what I should do. Thank you