I had a client last year who developed hives mostly trunk and legs.  She was
breastfeeding her twins( and still is) which were 6 weeks old at the time and
she also had a three year old.  The cause was never determined, she was
placed on Prednisone tapered over 10 days and Atarax as needed for itching.
 Totally resolved within the week.
 I told her it was most likely that she was allergic to cooking, cleaning and
doing laundry and that she should stop doing those things immediately !
(Ha-Ha)   Needless to say she was also advised to wean by the dermatologist
but didn't.

Maria Parlapiano RN, IBCLC
The Lactation Resource Center, inc.