Gloria is poorly

Hello everyone.
I havent posted much on here and i'm a bit of a lurker but wondered if you could help.
My 20 week hen Gloria is looking a bit poorly.
She hasnt ever laid me an egg but is normally full of beans and character chasing me round the garden etc. My other girls laid for me from day one. I just assumed as Gloria was a few weeks younger she was just a bit slow to get started. Today she is kind of just 'hanging' about looking miserable. I've just watched her fall asleep in the middle of the garden (very unusual) She has a semi arched looking back. I dont know how to describe it , a bit of a hump. This goes when she walks although shes doing this very slowly. She is half heartadly pecking about but not as much as usual. She is basically looking a bit confused.   
I'm not sure what to do. I feel very worried. I'm having to stop myself for bringing her in and tucking her up in bed with the tv on 
Any ideas? she looks very healthy apart from her odd humpy back and her worried little face
Thanks x

poos look normal and I think she is drinking lots as normal but I will keep a close eye. Do they sometimes go a bit odd when they are about to start laying? This is the first time ive kept hens so although ive read as much as possible I'm still a bit clueless.

Sounds very familiar symptoms as 1 of my girls, all the others laid their 1st eggs without much trouble but Layer went really withdrawn hunched up like you describe  but still eating and drinking poo's normal etc. then a few days later started to go in and out of the nest box, then finally she laid her 1st very small eggie! on the run floor!
Bless her! she looked shocked and relieved all at the same time! finger crossed this is all it is with Gloria!

Debbie x

thanks everyone, you've made me feel so much better. She is brighter today and like you said she has been going in and out of her nesting box- obviously trying to work it all out for herself. It never occured to me that hens got PMT.