Nipples different this time around

With my first my breast didn't change much at all other than going a bit larger and areola only a shade darker but my actual nipple never changed...
This time (2nd baby) my breast have grown soooo big, areola are super darker and bigger and my nipples are also a lot bigger and always erect. 
Any reason why it's different this time around? Do you think it could be my body knows what it's doing this time around or maybe being older (was 18 woth first now I'm 22, 23 Tmro)