Help! Duck acting strangely!

Hi All!

I have 2 6 month old female white pekins. On Sunday evening I went up to the run and one was kinda laying in the corner, really lethargic, kinda holding herself in a weird posture and her quack is very hoarse - almost like a bull frog. These are my first ducks but I do believe them to be both female - I get 2-3 eggs everyday but never see them laying. So I was reading on different sites and I thought maybe she was egg bound. I could never find evidence of an egg however and I had gotten 2 eggs that day. I expected to find her worse or dead the next morning but when I went up to let them out of the coop on Monday morning - nothing was amiss. She seemed totally normal. So I just assumed it was a passing thing. Has been normal since! Well tonight I go up to shut them in the coop and its the same thing! She was in the corner by herself, very lethargic, lets me pick her up and hold her however I want, croaking more than quacking, laying her head down, etc.

Im perplexed! I cant find anything with these exact symptoms. Has anyone experienced this before? Nothing has changed in her environment - they have a coop and large run that they share with chickens. They eat Layena crumbles and dont free range although I provide them grit and treats - but no new treats of late.

Its strange how she was so ill seeming and then fine for three days and now all of a sudden after seeming normal all afternoon - she is acting poorly again.

Anyone experienced anything like this?

Thanks in advance!