Poorly chicken

Ive had my three girls for three months now.
They are due to be wormed and I have Fluvenvet on order,however Sage is looking awful.
She does squirty yellow/white watery poos,sometimes with small streaks of yellow in.
Overnight,the other two poo nice neat poos and where she lays hers are yellow/watery.
Today shes lethargic,drinking and eating a warm mash but not herself at al.
Anything I can do?She has a very messy bum and Ive sat her in warm weater which she loves but its not helping her when she gets outside again.She doesnt seem to like laying down much either..Help!I dont want to lose her
 

Thanks thats what I thought-will book her in tomorrow