Well, it's good that everything in your tank is in order. Have you had the fish for a while? If it is new, the stress from the move may still be an issue. If not, then I'm out of ideas.
One other thing...do you add aquarium salt to your tank? Mollies appreciate some aquarium salt in their water...about 1 tablespoon per 5 gallons. Make sure it is aquarium salt, not just table salt.
That's all I've got for the moment. Keep us posted on how your fish does. Hopefully the MelaFix will do its job and you'll have a happy, healthy fish in no time.