Insufficient data, stoned. How old is the tank, how old are the mollies, how big is the tank, what other stock does it include besides mollies, how many mollies total (adult I mean; if there are fry and you don't have an exact count give a guess rounded to the nearest 10), is it planted etc? Has anything been added or removed in, oh say the last month? What decor, rock, wood and plants do you have and are the plants live or fake? (I am assuming live ones as you say "planted tank" but I have seen people use that phrase with fake plants so figured had better ask.)
How often and how much % water do you change and when was the last one, do you have water params, how long ago was the test done and with what testing equipment (dipsticks, liquid test kit, test done by LFs etc). How much and how often and what do you feed? Have you ever observed any aggression in the tank and who was perp and who was victim if so?
Do you have a QT tank set up or could you set up an improvised one with equipment on hand? It is always better to remove sick/injured fish from the main tank; it gets them away from whatever the source of the problem might have been, it prevents other fish from being exposed to possible disease; and it's way easier /cheaper to medicate a smaller water volume than a big one, not to mention it places the medications right on the victims rather than exposing others who don't need it.
that will do for a start. Give us the bigger picture, your description is too short to enable any advice to be given. Best regards to you and the fishy ones...
