I suspect it is related to the hormonal changes that occur in conjunction with your cycle. The itchy may be from yeast and may respond to diflucan, an anti-fungal, but especially to a change in diet. Denying it the sugar it loves. A gynecologist may be a better resource for this question.

This may be a question better answered by Ob/Gyn. But I can only assume it has to do with the change in hormones during your menstruation cycle and how your breast tissue is responding to those changes.