Sick Chicken ?? Help please

[oma4630]

I have this chicken, 8 weeks old ( Welsummer or Brown Leghorn) that seemed very lethargic 2 days ago. It ate very little and was very listless. It perked up some yesterday and when I brought treats did come up and pecked at them - but not much and walked away. I lays a lot and perches a lot away from the other and is still very listless and slow moving.
Any ideas ?? I sure don't want to loose this chicken which I have named Pretty Girl.
Thanks for any advise.