Shaky Chick

[Fraoch21]

I have a 5-6 week old sablepoot which shakes all the time. Today she has just developed a limp for no apparent reason and tends to lie down a lot. She is very tame and when I hold her with my hand over her back she stops shaking but starts as soon as I take it off. Is this a nervous disposition or something, any ideas?
Thanks!

 

[Fraoch21]

I forgot to mention a few more unusual things that might be helpful. She does a yawning motion quite a lot and sometimes when shes sat still and you listen to her breathing it sounds kind of crackly and popping?