What other things could cause sore nipples besides pregnancy?

Sore: Reasons for painful breasts (bilateral) can include: cyclic pain before the period, stress, medication changes. Fluctuating hormone levels & pregnancy. Pain in one breast could be related to a cyst or a fibroadenoma. Breast cancer would not be a frequent reason for breast pain. Exercise with a bra that is lacking in support is also a possible cause. One reason for nipple soreness is friction.