Why when I breath do I smell Ammonia in my nose?

Yes I have experienced that too. Sometimes when I work in a chemistry laboratory and too much ammonia is released in a reaction, I smell Ammonia for like the whole day. I think its just some brain trick.

Another reason could be that your toilet is not cleaned properly and ammonia is released from there.

Also sometimes smelling Ammonia all day can be a symptom of Liver or Kidney disease. I would say you should consult a doctor if the smell is too persistent.