Yesterday I noticed that my left nipple hurt when I touched it. It feels tender and my right one is perfectly fine. When I rubbed my left nipple, I felt a little ball or lump underneath my nipple that I could move. I woke up this morning and it was still sore and is annoying to touch. I've read that it could be a sign of puberty, and I am an 18 year old later bloomer who is due for some change. So is this most likely associated with puberty, or is it something much worse?