The white spots are symptoms of
ICH, also known as White Spot. There are some medications you can buy to treat it. Adding salt will help, too. Mollies like at least 1 teaspoon of aquarium salt per gallon (not marine salt or table salt). Ich/White Spot is usually not fatal, but you should start treating it ASAP. Have you been testing your water? More info on your water perameters would be helpful. If you haven't been testing it, you can buy a kit of test strips for
pH, hardness,
alkalinity,
ammonia, nitrites, and nitrates. Also, try to move the fish to a bigger tank--10-gallon or bigger is best. The problem with smaller tanks is that if you are using a heater, it is probably cooking your fish; if you are not, your fish is probably too cold. And do you have an aeration system? If not, when you're fish was hanging around the surface he was probably gasping for oxygen. The
water change would have added more oxygen to the water. Buying an air pump, tubing, and an air stone will solve this problem.