Why would my nipples be hard and sore for like a week now?

Nipple soreness: nipples are sensitive to hormones, and may become hard and irritated if you are pregnant. they may also develop a dermatitis, from detergents used to wash your bra or undershirts. They could be irritated if another person or an animal plays with your nipples or sucks on them, You can use hydrocortisone cream 1%, twice a day, and do a pregnancy test. If not better, go see your doctor.