Hi! I'm a sixteen year-old boy, and I noticed a small bump on my tailbone couple weeks ago. It is the size of a marble, moves very easily. The bump is not painful at all, it's not red or visible in any way. I have been googlin about this, it could be Sinus pilonidalis. I have bad case of cystic acne, first I suspected it to be a normal cyst but it has no signs of future bleeding or 'popping'. The bump is right below my tailbone - when I lay down it's right on top of it, and it moves a lot! Almost half an inch to the right, under my skin.
Can this just pass by itself or should I see my school nurse?