G.B.
Certain bras that i own will cause me itching in that area.
Sometimes it can be that you are using too much laundry soap and it is irritaing the skin. I never realized how much laundry soap stays in washed clothes, until we had a spa with a super jet. When we wore (clean) bathing suits , it caused soap bubble buildup galore (PILES OF BUBBLES) in the spa.
Tea tree oil is what I use for yeast/itch issues on skin. Swab it twice a day.
If it is not gotten somewhat better by a few days with tea tree oil, I would go to the docotr. There is a form of breast cancer that presents as a rash on nipples or breast skin. (google it).