Welcome to the forum Gaf. Sorry to hear about your platies. Can you give us some history on your platies so we can be more help? For example, these questions would go a long way to helping us help you.
How long has the tank been set up?
What is your water maintenance routine?
How large is the tank and what all is in it?
What are the symptoms that the fish are showing, besides some kind of bloating? When did the fish first start showing these signs and what did you do right before that?
Have you tried a large partial water change yet?
Have you recently done any maintenance or cleaning on your filter?
What are your ammonia, nitrite and nitrate readings?