Getting a headache while driving.

[exdrocca]

I got to take the truck for a good drive this weekend. I noticed I was getting a slight headache. I'm thinking there might be some obnoxious fumes getting in the cab. I don't have an exhaust leak that I can hear. It doesn't smell like coolant. The exhaust exits in front of the rear tires. I'm sure I'm burning a bit of oil, and might be running rich, but man it was kinda getting to me. Anyone else have problems like this?