IT probably is just the price you have to pay at the pump is more than you are used to.My local gas station went from $2.99 @gallon to $3.08 @gallon OVERNIGHT!!!!
Needing a tuneup
Does it have a plugged O-two censor?
Prices are going up all the time,maybe that is the answer.
As the price of gas goes up it becomes a more valuable commodity to steal. Maybe someone is siphoning gas from your tank at night...buy a locking gas cap and see what happens to your fuel consumption.
I'm not a mechanic like insomniacSeven, yet my guess is to have a different mechanic do an overall check of your car. Maybe something wasn't hooked back up properly when they changed the alternator. I had a mechanic put a new tire on the wrong way when they checked my brakes. When I took my car in again, another mechanic caught the mistake. My tires are all black and it wasn't that noticeable. Maybe my original mechanic was in a rush or distracted and made the mistake. That is possible for you too.
maybe you have a leak in your gas tank
If I had to guess, it's the O2 sensor. Is there a "check engine" light?
change the air filter, fuel filter, change the oil, get a tune up, make sure the tires have the right pressure and use a fuel additive.<br />
and drive more cautiously, if possible.