Some ideas (I didn't check to see how they/if they interact with breastfeeding) are:
eucalyptus
red clover
alfalfa
licorice root
apple cider vinegar
Dulcamaral (comes from Bitter sweet plant)
teas made of ginseng or borage (boost the immune system)
actual homeopathic remedies, like allium cepa, Euphrasia, Natrum muriaticum (can be found at Whole Foods or your local co-op, community pharmacy, or whoever sells naturopathic remedies.
Best bet would be to find a homeopathic practitioner who practices homeopathy who can help you by effectively finding what will work for YOU and your symptoms because every person is an individual; what works for one person might not be what will work for you.
Another suggestion would be to cut out drinking and eating cow/dairy products. They produce a lot of pflegm and coughing, etc. You might find some relief that way.
Good luck!