pufferfish

Question
I bought a freshwater pufferfish from Walmart this past week, and we put him in a tank with a filter system and before we put him in we added "start right" to clean the water.
The first couple of days he did fine and would sleep or relax on the bottom of the tank with the rocks, but if you moved the tank or put your hand up to the glass, he'd move. And if we wasnt laying on the bottom he was always swimming around.  
Well I've never really seen him eat (I put the tropical fish flakes in there, as thats what the store said to feed him, along with small shrimps) but I've never seen him eat.
Now today he's just lying on the bottom and if he moves it's lethargically and he's not swimming around the tank constantly. He keeps low and doesn't swim to the top.
I called petsmart and they said that most fish from walmart are sick, and to make sure the water is room temperature and to use the start right formula again to make sure the water is clean. Well I did that, but he's still not back to his chipper self.
It sounds to me like he's sick, is there anything else I can do to get him to get well? And should I try feeding him something besides flakes? Or is it likely he just eats when Im not watching him?  

Answer
Well it sounds like he is stressed from the journey and is getting used to his surroundings if he doesn't eat within a day or so try the shrimp you were reccomended but he might be sick but look for signs white dots, and unusal things. But watch him and see if he eats but it si normal for him to move if he sees a moving hand he is just scared thats why he swims around he should be fine within a few days.