To help you out we need more concrete facts instead of putting $40 of gas every two days and that you consider yourself a normal driver. You say you average 60 on the freeway, but how many miles per day are freeway vs. stop and go city traffic? How much traffic are you sitting in while in LA? Are you running your AC? Stop and go conditions while using the AC eats gasoline like a fat-kid eats Twinkies.
But still a good idea to get everything checked. How many miles total on your 3? This alone could help in guiding you to what's potentially going wrong be-it bad spark plugs, fuel injectors, poor tire inflation, etc. There are a lot of variables to could contribute to poor gas mileage, some mechanical, some electrical, some due to neglect, some user error.
Also try this, the next time you top off your gas tank, reset the trip odometer and at the end of each day write down how many miles you've driven. Start keeping track of the numbers. It helps, when you start to see the numbers change then you know something is wrong with your car. I've got a free app on my Droid phone that keeps track of every time I put gas in the car, calculates my average mileage, as well as reminds me of oil changes and the such... its a great tool and you see where your money is going, and most importantly you see when/if your mileage starts to go to shit...
Just my $0.02
-Mike, USMC, ret.