Hi, Infection of gums and sinuses may be some of the causes, which may give you a metallic taste and chemical odor in your breath. Your sense of taste is closely related to your sense of smell also. When your sense of smell is distorted, then your sense of taste is also distorted and may cause a feeling of nausea as is present in your case. However, if you are not having some physical reason for this and all your tests are normal, then it may be an olfactory hallucination or phantom smell (Phantosmia). The smell in this case may be long lasting or just a come and go type. Also it may be present in one nostril or both nostril. This smell differs person to person and may be pleasant or foul. However, this smell is usually unpleasant like metallic smell, smell of chemicals or like smell of burnt toast. Therefore, in my opinion, you may be required to see some psychiatrist for these symptoms. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Satnarain Bansal, General & Family Physician