Why does it feel like there is a rock under my niiple(male)?

about a month ago i started feeling like there is a rock under my nipple. i don't know what it is or how i got it. my health cles have never told me about this either. it happend around a time when my friend gave me a "purple nurple" and the next 5-7 days later it came up. i thought it was my body like healing it or something but its still there after a month. and it hurts when i putt presher on it. i am 13 and going threw male pueberty.