My Americana is acting weird?

[h.woods54]

I have 3 pullets, a R.R, a Plymouth Rock, and my Americana, all turned 6 months on Dec. 5th. The R.R. and the Plymouth Rock have already started laying, but the Americana is acting weird. I'm confused as to whether or not she's depressed or egg bound. I originally had 4 chickens, one turned out to be a rooster and I had to find him a new home. The R.R. and Rock seemed to have bonded and would never leave each others side along with the Americana and my "roo". When I found him a new home, my Americana acted as she usually did, running around, eating like a little pig, stealing food from the others. About 2-3 weeks ago she stopped acting like she normally would. Maybe she has fallen down in the pecking order? I'm just worried that she is sick, I checked last night to see if she was egg bound but came up with nothing. She also goes to bed early, as soon as the sun starts to go down, she's in the coop on the roost while the other two are still running around and eating.