What Are The Pimple Like Rashes On The Breast Cleavage?

I am breastfeeding my nine month old almost exclusively and have recently developed a rash between my breasts, in my cleavage. The rash is a small pimple like rash that does not itch but also has not cleared up despite exfoliating and keeping the area dry. I am worried that it could indicate inflammatory breast cancer. Could it just be due to fluctuating hormones due to breastfeeding? I have just resumed menstration.