Nipples

My nipples are EXTREMELY sensitive. Like I can't even stand one gentle touch from myself or my partner. It's not a bad sensitive though, it tickles and it feels really really good but only during sex. Other times it just feels annoying and uncomfortable. It comes handy while having sex it's the #1 way for me to get aroused but other times it really does bother me. Why are they so sensitive? They've been like this for ever