I have a bad smell in my nose and can taste it in my mouth.?

This smell feels like it is suffocating me. The smell smells like melting plastic and comes and goes. When it comes I often choke or cough. No one else around me smells what I smell. It is annoying and sometimes scary because I feel like I cannot breathe or cannot get away from the smell. I sometimes can taste it as well. It is horrible and would love to know what it is. Can anyone help?