Your dog is not suffering from anything if it vomits once in a while no matter vomit is whitish or something else. There is possibility that your dog has eaten something wrong that is irritating it and will come out when it will throw up once or twice, Secondly on eating too much, dogs often get in trouble due to acidity in the stomach and this vomit their food out. It is suggested to reduce its diet to twice a day, morning and evening. Let it eat its favorite food, an do not try to change that for a while.