A thing you might want to check since your car seems to be the only one in the area that is fogged up on the inside.... Lift your mats and make sure they are not wet. It sounds like you might have a wet floor mat or hopefully not a leaking heater core which will give you a oiy film on the inside of the windshield. Another anti-for trick from the days of the old model "A" Fords was to use a damp cigar and rub it on the glass. Since this can be messy I woulden't suggest that but at your local auto parts look for Rainex brand, (the people that have the treatment that causes water to bead so you don't have to use your wipers unless it is pouring out)They make a anti-fog treatment for the insid of the glass on cars. Scuba divers spit on their face masks to keep them clear and I woulden't suggest that either.
Good luck,
Dennis