Ductal yeast can definitely occur in only one breast.  It is hard yet
to determine from what you said that this is definitely ductal yeast.
Such pain may be radiating from a sore nipple, at least that is what
everyone says, though I don't understand why it would occur when the
baby is "not" nursing.  Raynaud's phenomenon (with a blanching nipple)
can give the same sort of pain. There are undoubtedly other things,
but I don't know what they are.  Such pain which is not Raynaud's, I
treat as if they were yeast.

Jack Newman, MD, FRCPC