Cancer including breast is very rare in someone your age. But it is important for women of all ages to be breast aware and to report any changes in their breasts to their GP. It is always advisable to get a quick breast check done. Your doctor will be able to examine you and advise you further. If they feel this needs further medical assessment, then they may refer you on to a breast specialist at your local breast unit. They may suggest that they might want to examine you again just after your next period, to see if the small lump under your nipple is related to your monthly cycle.