What Causes Sour Smell And Itching In The Breast?

Hi, I am 37 with 3 children and my breast has dropped alot after the last 2. I have a sour smell under my breast which also itches alot and has become dark. I use a powder after my bath to help with the itching and to keep away the smell but this only helps a little. I would usually use sudocrem cream and this will clear up the darkness but the smell is very strong. Is there something else that you would recommend?