My nipple is always sore and hard?

My right nipple consistently hurts and is almost always hard to some degree, especially compared to the left. The left is soft usually, but the right almost always hurts a little and is really sensitive to pain. I thought maybe it was a sexual thing, for the first while, as I have a somewhat active libido and masturbate semi-frequently, but even when I tend to stop, and throughout the day even, it remains the same.

I'm still facing the last stages of puberty, so I assume it may have that as a factor, but... generally, is it normal for just one to always be hard and sore?