There is a plus and a minus to report. First it must be said that for some moms, breastfeeding sessions can trigger a sensation of nausea over and above regular morning sickness. Let-down in particular can bring on a feeling of nausea. On the plus side, many moms seem to suffer less morning sickness over all when they are breastfeeding. Indeed, some moms say that when they weaned the morning sickness hit the roof. (Does breastfeeding really reduce morning sickness? Sure seems that way, but only a study can tell us for sure.)
It can be very overwhelming to care for your child when you are nauseated and tired. Try different techniques for minimizing morning sickness, maximize nutrition when you are able to eat, and be creative in finding ways to adjust breastfeeding to minimize your discomfort. Making little adjustments both in how you arrange your nursling and how often/how long you nurse can sometimes help a lot.
Positioning changes can be helpful for increasing mom’s comfort. Often the worst position for nursing when you are nauseated is when your child is resting on your belly. When you are sitting, can your child sit next to you, with knees pointing away? Does your child like side-lying? When you’re on your back is there any way to prop up your child’s body on a pillow alongside your body, so your child can still be “nursing from above” but not perched on your poor belly? Also, some moms find that seated nursing reduces nausea.
Some moms find that they can work through the nausea by making adjustments in nursing; others find that reduced nursing or weaning is ultimately for the best.
Adventures in Tandem Nursing by Hilary Flower also has excellent information on pregnancy nausea and vomiting, including information on keeping pregnancy nausea to a minimum and maximizing your calories.