5 days is not unusal for an ig in new settings.
try covering the area of the cage where the food is so he feels safe to eat. Try grapes or strawberry.
Other things can play into not eating also, for instance, illness or a cage being to cold.
If you post pics we can tell you some things, if hes thin, if coloring is off, things like that but your best bet is a visit.
Post pics anyways tho coz we like looking at igs :)