have you put them straight in with other hens?
sounds like you'd be better isolating the new ones, until you're sure they are not carrying anything infectious.
how do they look? any particular posture to them? any eye trouble?
how have you treated them... I mean, what with? worm treatments are often dosed so many days apart, so you may not see a change straight away.
what breed are they? (just being nosey now!)