There is a hard lump on my tail bone right at the start of my but cheeks, it dosn't feel like its right under the skin, it feels like its on my bone. This is my 3rd day with it there, it hurts to sit down and do other things. I am 12 and not sexually active or anything else. I dont remember falling on it but it hurts to touch. Its about 3.5 cm. in diameter and not a complete sphere, just round. Please tell me what it is and if I should be concerned