The main two reasons your breath might smell of metal is: Bleeding or bacteria.
Blood often has a metal/iron taste and smell, and this could be happening in your mouth due t bleeding gums (perhaps gingivitis) or a cut or ulcer...
The mouth is also home to a wide range of bacteria ( the mouth contains more bacteria than even the anus), so it's possible that some sort of bacterial infection is causing this smell.
See a dentist or a doctor as soon as you can, as symptoms like this should be checked out!
You can also purchase certain dental hygiene products that should help with the smell in the meantime.