My two week old baby has a hard enlargened breast. only her left side and this was a sudden occurrence. she is fussy and crying more than usual.

Possibilities: In the womb, an amount of maternal hormones that maintained the pregnancy entered & left by the placenta. After delivery, some are left behind & can cause breast enlargement on either sex usually on both sides.These breasts can occasionally make a milky substance. Rarely germs can enter through the nipple ducts & trigger infection. If there is any redness this should be evaluated immediately.