If it were ME and I was suffering with allergies and breastfeeding, I would NEVER trust any medications, prescribed or otherwise. So many of these a new and they just do not know the long term effects on adults - let alone infants.
The most non-invasive thing you can do right now is to use a neti pot with saline solution. The first few times you try it, its going to be hard, but after that, it gets easier and easier. Then when you are done with the neti, follow up with a few sprays of xlear sinus spray. It is a saline based spray with xylitol.
neti pot http://www.healingdaily.com/exercise/neti-pot.htm
xclear http://www.xlear.com/articles/nasal-spray.aspx
You will be amazed at how much better you feel if you do this regimen a couple times a day. I used to be the poster child for allergies and sinus infections. Not anymore.
Mix up a gallon of saline and keep in the bathroom. (4t sea salt, 4 t baking soda) Then you will be more apt to use this everyday.
Watch your dairy, white flour, white sugar and orange juice intake as these are all mucus makers.