Electric yellow not doing too well

hi guys, I got a 5 inch E. yellow a couple of days ago from the fish shop. I
think it is a female. It is not in very good shape.

when it hovers still in the water it is not quite horizontal, it's head is
higher than its tail, on a ~ 25-30 degree angle. It also uses it's "cheek
fins" (the ones on the side of it's body) more than the other fish, so it
looks like it is struggling slightly to keep it's balance.

It's gut is quite concave and hollow looking, it has taken a little food,
but as it is only 2 days old in the tank, it hasn't started eating alot yet.
I am hoping once it has a gut full of food it's balance/bouyancy problem
might go away??

it also has quite a pale face, almost white, and it's body is paler than the
other big yellow I have in with it.

other than this it seems ok, it swims around and stuff.. when I first put it
in the other yellow, that I know to be a male, immediately went for it, and
he chased "her" around in a circle at a hundred miles an hour. (looked like
a dog trying to catch it's tail). he then chased her around for a while, but
now he tends to just get in her way as she is swimming past and showing
himself off to her. so he seems to think she is a female at least!!