Wondering why my new bearded dragon wont eat..?

\I got him on Thursday, he's a pre owned pet. They said he's 9 months old and eats well. I got him home and i'd had him out a bit too long and he went really quiet and his breathing was labored. I put him in his viv as soon as i could and his eyes were shut, after about an hour or so he woke up and started to move a bit. He ate one or two meal worms and then i left him, giving him time to relax after his move. The next day i put some more meal worms in and he didn't eat them, i put some more in the next day seeing as the others had gone and he didn't eat them either. I got him some lettuce and he munched that down... More lettuce today and he ate that but he's not eating any insects or meats... I'm a bit worried i'm not sure what's wrong. Please could you help? Thanks. (: