sick or pregnant fish?

Question
I have a 55 gallon tank with 2 mollies, male and female, 3 silver dollar fish and a plethemous (spelled wrong!). Several weeks ago I treated the tank for ick. One fish died, but the rest have been doing well until a couple of days ago. One of the mollies is laying at the top near the heater. The sick mollie will eat, but it spends most of the time bent in half at the top of the tank. It looks to me like the fish is breathing heavily too. I called the pet store and they suggested I do a water change. I explained I already changed the water when I did the ick treatment (because that is what the directions said to do). So then the pet store told me to try the fish in another established tank. I put the mollie in another tank in a breeder box because the other fish were nipping at the mollie. That was 24 hours ago and there is no change in the mollie. Can you please help? I really want to help this fish.  

Answer
You did not mention if the abdomen was swollen at all which would have indicated a possibly pregnant fish. It is very abnormal for a fish to be bent in half. With not being given any obvious problems on the fishes body I am left to believe this may be an internal illness. Something you can try to do and see if helps is add some regular aquarium salt to the tank your ill mollie is in, as mollies typically do better when there is some salt in the water anyway and it will help lessen the stress for the fish. The fish shouldn't be breathing heavily as you described, if the fish was doing this in the medicated tank it may have had trouble getting oxygen out of the water but should be ok now with no medication in the tank its currently. I wish I could be of more assistance but internal are always much more difficult to take care of as you can not see the cause. I wish your little fish and you the best of luck.