Stinging nipple (not pregnant)?

when i woke up this morning i noticed my nipple was stinging on and off it's been like that for the whole day and it's so anoying. i've been looking on google, and everyone that has this is pregnant, which doesn't help because i'm not pregnant.i did think it was an irritatation from my pajamas but i know it's not the fabric softner or soap cuz ive been using it for 6 years and it hasn't happend before..