Hi i am Dr Ahmed Aly thanks for using healthcaremagic site , I had gone through your question and understand your concerns .. In my opinion i thing your viral infection still not completely cured causing your flu breathing problem and thus causing the metallic gases flavor . Your back pain could be a kind of muscular spasm trated by painkillers when needed , hot massages with topical gels , muscle relaxants , avoid heavy lifting and vigorous movements with some bed rest will be enough . For now i suggest some nasal steaming with minor medications as viral infections doesnt need antiobiotics , Z pack , paracetamol , antihistaminics for your flu . If your back pain persists visit your physician for proper evaluation of the underlying cause . Please click THANK YOU and consider a 5 star rating with some positive feedback if the information was helpful. Hope the above information helps you, Any further clarifications feel free to ask.