What's a good cough medicine for my 4 year old? she has bad allergies but the zyrtec (cetirizine) isn't helping. she also ran a low fever.

Her cough : Is more than likely from her postnatal drainage . If she does have a stuffy nose and chest congestion ( noisy breathing , wet cough or a rattle in her chest ), you can give her Mucinex (guaifenesin) 1/2 teaspoon twice daily for 2-3 days and see if it helps. Take her in, if her condition gets worst, start wheezing , fever going up and not eating or drinking or if you are concerned!