Baby bearded dragon eyes closed?

I just bought a bearded dragon for my brother from the pet store and Im taking care off it till he get back from his vacation, since I already have a little experience because I own my own beardie since he was like a 2 weeks old this one is about the same age as that cause for some reason the pet stores sell them very very young . When it was in the box on the way home it was really alert but every once and awhile closed his eyes but I figured its alright cause he was is the box for awhile. I fed him when it just got home and the little guy ate 5 pin head crickets right away but when I put him in the aquarium he shuts his eyes all the time, then when i take him out he opens them for like 20 seconds and is all alert and looking around being curious, then closes them again. Any one have any ideas? if it was sick could he even open them at all and not be all alert like he does, or is the lights too bright?