Pseudoephedrine (Sudafed, Actifed) yes L3 (moderately safe) for acute use
L4 (possibly hazardous) for chronic use due to potential for decreasing milk supply
Pseudoephedrine & milk supply: Thomas Hale Ph. D., a renowned breastfeeding pharmacologist (Breastfeeding Pharmacology), notes that "breastfeeding mothers with poor or marginal milk production should be exceedingly cautious in using pseudoephedrine" and that "it is apparent that mothers in late-stage lactation may be more sensitive to pseudoephedrine and have greater loss in milk production" (Medications and Mother's Milk, 2006 edition).
If you do take pseudoephedrine and notice a drop in milk supply (many moms do not, but research shows that it can decrease milk supply by as much as 24%), simply stop the medication and take measures to increase milk supply - the problem should resolve fairly quickly.