For About A Month I Constantly Smell Exhaust Fumes That

For about a month I constantly smell exhaust fumes that aren't there. I have 3 brain aneurysms and headaches that my neurologist has me taking topomax for morning and night. It really does keep the headaches at bay. Now I'm reading this is not uncommon, but can be anything from allergies to vitamin deficiencies to celiac disease. Any ideas?