It is possible that the oil previously in the engine was 0W-20 (if that was the oil from the factor) so that would save a bit of fuel when the engine is cold.
If you have been doing more short trips and or stop and go driving than than before, that could account for the increased fuel consumption. If you have found yourself in more traffic than usual, that could account for the increased fuel consumption.
If the temperature has dropped, the fuel consumption will increase on startup because the engine will run rich when it's cold. Rich mixture is more stable than stoichiometric or lean mixture.
Since you only got 23 MPG, I assume you are doing mostly city driving or lots of stop and go. I drove 180 miles in my 2007 I4 Camry and used just over 1/3 tank.