Im a 16 year old boy and my nipple has swollen and a small hard thing has grown under it, can anyone help?

Transient change: About a half of males will undergo a transient nipple/breast enlargement at the onset of puberty. Normally it will resolve slowly as other hormonal changes kick in over about a year. Less often it can persist over 3 years and surgery may be needed for cosmetic improvement. Carrying around extra weight can aggravate the issue as fat can masquerade as breast tissue.