Their is a dr who only deals with medications in mothers milk. His name is Dr Hale. This is his web site
He will email you if you need him to. He has a book and a ton of info. Just look at his book. Your pediatrician should have it.
I take ALL SORTS of meds and nurse. Some of the medication I need is less common so I talked to Dr Hale and he said it was fine! Most medications get into the milk in such a small amount that it is ok. Not all of them though.
So if the one you take is bad then see if you can take another one till you are done nursing.