>>What would I be thinking?  Mechanical trauma of some kind, muscle spasm in
the chest wall which feels like its in the breast.  Bacterial infection.
Chronic inflamatory mastitis.   I have had a few women who needed to do a
unilateral weaning.  Maybe that would be worth a try.<<

I have been thinking the same direction as Barbara. You might also inquire
on fibromyalgia and some of the other autoimmune mystery illnesses that can
impact breastfeeding, and also gently explore for any psychological issues
with breasts/mothering (a long shot, but sometimes occurs).

Lisa Marasco, BA, IBCLC
Santa Maria, CA