drop in mpgs?

[TheDon]

I drive 90 miles 2-3 days a week to class. That is roundtrip. Lately I've noticed my mpg's drop. Now, my odometer doesn't work so I am gauging this on how many days a tank will last me.

Example, monday I had half of a tank and drove to school, then to the other school, then to the gym, then home. Total mileage.. 106 miles -ish. I blew through a half tank of gas which I then filled back up to half. Around 10 gallons from reserve light on to the half mark.

my driving style is relaxed, I don't speed, accelerate like crazy, or idle for long periods of time. The drive is 80% highway 20 % not highway (not exactly city driving).

What is going on? I need to get my odometer fixed of course. Please donate to the Help TheDon foundation by clicking this link.. ha

Other than that The air filter isn't gunked up, I'm not leaking fuel, I just put in a working MAF, the check engine light is not on, my tires are properly inflated.

I don't get it?