Flange issue

I was using a 27 shield but felt like a lot of areola was getting sucked in. It didn't hurt but by everything I saw I didnt think they were the right size.

I went to a 24 and my nipples swell and crack and turn red.

And went to a 21 and now they are turning white however it feels more comfortable (other than the itchy nipples lol)

I can't really tell a difference in my supply with the 27 and 21 but did notice is lessen with the 24 but could have been a fuke.. Im at a loss.