Wood burning fireplace

So we have a wood burning fireplace in our main living room where my 7 1/2 month spends most of her time. We haven't burning anything in it since before she was born, but depending on the weather I can smell that sooty fireplace smell a couple times a week. The flu is always closed, and the whole thing has been cleared of ashes and such. My daughter has had a stuffy nose for almost 2 months and it has been keeping her up at night a lot. I'm wondering if anyone has any suggestions or knows if this could be a reason as to why we can't get rid of her congestion.