I've Been Smelling Exhaust Fumes For A Couple Months Now.

I've been smelling exhaust fumes for a couple months now. I'm not around a car or garage. It gives me a headache and makes me sick to my stomach, as if I'm really smelling exhaust fumes - but I am not around anything emitting exhaust. It happens when I'm working at my desk, watching tv, at other people's houses, etc.