Hello,
It looks like nipple dermatitis which has been aggravated by tight bra, hormonal changes and cold and dry weather which could have caused minute cuts on nipples. If there is any redness then you may apply topical antibiotics like Neosporin. Also consult your gynecologist to rule out galactorrhea and wear cotton undergarments.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Your obstetrician is the one to call for this. I'm sure it's a hormonal thing, but he or she is your expert for everything.