My little boy was weighed for his 2 week check up yesterday and he was even less than his 2 day old weight. Why is he still losing weight??

I had some problems establishing feeding but all seems to be going well- he feeds regularly, sleeps contentedly, has wet and dirty nappies... I don't get why he would still be losing weight. I know you shouldn't base too much on weight and I don't mind that he's not back at his birth weight (as they are 'supposed' to be at 2 weeks) but to have lost more really concerns me.

Anyone else's baby still losing weight at 2 weeks but no problems? I'm concerned maybe I'm not making enough milk still, or maybe he's not sucking properly?