Yes, I had hay fever whilst breast feeding and I asked the pharmacist and you can get a safe hay fever medicine. It's in a pink box, just check with the chemist. ☺
Google "mothersafe hayfever" - you will find a factsheet published by the the NSW royal women's hospital on all the available medications and what's safe whilst pregnant or breastfeeding. it also provides references if you want to check out their data further :)