There used to be a woman on here with the name "Montezuma" who gave great advice on whooping cough. Maybe do a search. I don't believe she is on the forum anymore, but I believe her old posts can still be found and are very detailed and helpful.
Also, sodium asorbate is supposed to be great. It's a form of buffered vitamin C and comes in powder. You will probably have to special order this stuff, as I've found most health food stores don't always have it. Do a search on here and you can find some good threads for it's use. It's supposed to lessen the symptoms of whooping cough. Keep breastfeeding and make sure your baby is propped up while sleeping.