Tropical Fish Help Needed - Fish in Distress!?

Hello, are there any tropical fish experts out there? I am having a terrible problem with my tropical fish tank. Currently, we have three black mollies that are in distress. Their tails are hanging down vertically and they are straining to keep themselves up. The rear portion of the fish is literally vertical. Recently, we had difficulty stabilizing the tank after bouts with ich and a fungal infection. As the mollies are black, it is very easy to see diseases of this sort. I did not see any white spots on them until yesterday, when I saw some white around one’s mouth. Does anyone know what is causing this? Could it be a symptom of another fungal infection or is it unrelated? I began giving them medication for fungus infection, although I am not sure that is what they have. Am I hurting them by giving this medication if they do not have a fungal infection? Please help, it is sad to see such nice fish in such distress! Thank you. Laura