I'm sorry but i have skimmed most of this thread. I just have one question for you....
What the hell are you joining a gym for at 4 weeks post op? Are you serious?
Firstly, you shouldn't be thinking of serious exercise until your surgeon gives you the go ahead. I know quite a few wls patients who have hernias, and a sure fire way to get one is to be doing silly things like strenuous exercise without surgical consent..... Seriously suspend your membership or only use the pool till you are told otherwise.
As for weight loss, your body is getting used to the surgery, you have swelling going on inside you and probably still some anaesthetic lurking. Be patient. You aren't taking in many cals at 500 a day. I know eating is tough, but if you can't physically eat them then drink them. Get some good protein rich milk down you, good for healing and good for the protein...
Believe me, you can't be the only one who has thought they were the one to beat the bypass and you won't be the last.
Now get on with being a big loser please
xx