Several recent posts have related to nursing mothers experiencing nausea when
breastfeeding. This may be due to the sucking-related release of
gastrointestinal hormones in the mother. There is a significant rise in
gastrin levels which occur within 30 seconds of the onset of breastfeeding.
Changes in GI hormone levels in breastfeeding women occur as a protective
effect to assure adequate energy supply for milk production. The baby's
sucking at the breast activates the maternal gut endocrine system with a
consequent increase in energy uptake.

This increase in GI hormones could explain the problem. I have had a fair
amount of success with mothers by recommending the use of sea bands or sea
cuffs. These are elastic bands worn around the wrists with a button on the
underside that is placed over the accupressure points that reduce nausea.
These bands are often worn by people for motion sickness and can be found in
maternity catalogs.

An interesting reference for the changes in GI hormones is: Uvnas-Moberg K,
Widstrom AM, Marchini G, Winberg J: Release of GI hormones in mother and
infant by sensory stimulation. Acta Paediatr Scand 1987; 76:851-860.