large breast... rash

Lil0lin
So as the title says....
I've got large breast, they've gotten bigger now that I'm pregnant 
I notice that I'm getting a nasty rash under my left (aka the bigger one aka my husbands fav boob lol).  I've used baby powder made sure to keep it dry after I shower and even tried diaper rash cream lol!  
It's getting hot so I think it's just sweat, my bra and everything all adding up to be a mess. 
Anyone have any tips to get rid of the rash?
Thx u!