God_dammit

I have an 08 Cobalt, 2 door LT. I recently bought it second hand and its currently doing 8.3 L/100km (28MPG). When I first got it I wouldn't have to fill up for a couple weeks (at the time it said it was doing 7.9L/100km (29MPG)) Now it says 8.4 and I've verified that number is correct. I'm filling up more often than I should, three times in the last two weeks, my driving habits haven't changed and I do mostly city driving. I've looked online and it says it should be getting 5.9L/100km(40MPG). I'm wondering what you average and how far you go on a tank,

Thanks