What causes sore nipples for weeks?

Puberty can make nipples ache in female humans and some males.

Pregnancy can also cause nipples to feel pressure like clothespins for long periods of time.

There may also be a disease that has caused this. If the condition continues without cause like puberty or pregnancy, it may be cancer and should be checked by a doctor.

The only other option is if you had some sort of physical accident and hurt your nipple badly. Breast-feeding children may be enough to harm sensitive people.