What is safe to take for allergies (congestion, scratchy throat, sneezing, runny nose) while breastfeeding? Breastfeeding only once per day.

Use non-sedating. antihistamines that are available over the counter, such as Claritin, Zyrtec, or Allegra unless your infant is a newborn. You may find a slight decrease in milk production, which would be an issue if you are trying to build up your supply, but the trace amounts in your milk should not be harmful to your infant.