Believe it or not it is possible and, dare I say, common to experience such a discrepancy. There are a million variables that can each make a large difference, and they might all just be adding up badly for you. However, as somebody who is concerned about fuel economy it does seem quite unlikely that that would happen to you...if you were posting on RaceAroundLikeAJerk.com it would be more likely. Just keep in mind that it's possible.
Can you tell us about your car, roads, route, traffic conditions, driving style, and fuel filling procedure? Looking at your log, it does look like possibly short trips, which could contribute to low fuel economy.
What was your last car, and what was your fuel economy for that car?
Does your car roll well? If you put it in neutral while driving at a decent speed on a mild to moderate descent, does it coast at the same speed or even pick up a little speed, or does it lose speed?
Any warning lights lit on the dash?
This sig may return, some day.