sore nipples

Kaitlynn • Ellie Sue. Born August 20th, 2017 ❤️
I've had very sore nipples for the past 4-5 days. It hurts just to touch them. I've never had sore nipples like this or at all. It's beyond painful 😭 I took a pregnancy test but it was negative. What are other causes of sore nipples?