My One Moth Old Has Yellow Poop With White Stringy

My one moth old has yellow poop with white stringy seedy like stuff all in it. It's been like that since I can remember. She is formula fed. And I had her switched from the advance Similac to the sensitive thinking it would help but now I think she might have an allergy to the milk. ?? She grunts while eating now and nose is getting stuffed problems with her breathing her in there. Could you tell me if this sounds like it could be ? She fusses quite a bit .