You have what's clinically called an:
Olfactory Nerve Disorder: this means that something has affected the main nerve responsible for "smell"...which is why you keep smelling 'exhaust fumes'.
Here's a link:
Here are some possible causes: [I believe the nausea & headaches are related too]
I strongly advise that you make an appt for a detailed exam by a Neurologist; he will probably order some tests [eg head CT or MRI scan] to help establish the correct Dx, and then start you on the approp therapy.
I DO hope you found my Answer to be helpful regarding your medical condition. IF SO-please hit **ACCEPT** as you read this Answer. THANKS for your trust!
(feel free to ask a followup Q, if needed)
Best Wishes for Your Health,
--Dr. Steve, (Your Online Family Doctor)