What Causes A Pea-sized Lump Under Right Nipple?

My 13-year-old son noticed a pea-sized lump under his right nipple a few days ago. He mentioned that it is tender to the touch and hurts more when pressure us applied. Today when he pressed the lump, a yellowish fluid came out just above the nipple. I realize that breast tenderness and some swelling can be normal during male puberty. However, are the lump and secretion cause for alarm?