If you are coughing, strep is not very likely. Strep is usually sore throat and fever, and maybe nausea. Everything I have read says that when you have other symptoms, it is less likely to be strep. I would not take Robitussin while nursing. If it were me, I would call an alternative health care person that could tell me what to take while nursing. I would probably be taking high doses of Vitamin C and Sambucol, and probably some other things in my cabinet too.