Hello and welcome to the forum. Thank you for your question and sorry for the delay in response. First, that is excellent that you are performing self examinations on your breasts. That's a great habit to get into. My thought was you were beginning a premenstrual period which is when this happened. Hormonal changes at that time can cause this in your milk ducts. Did it go away? https://www.newhealthadvisor.org/movable-lump-in-breast.html If not, I'd think more like a lipoma which is a benign fatty tumor or a small cyst. Let us know if this went away.