Do you know if your current weight is healthy? "Underweight", "normal", "overweight", and "obese" are all labels for ranges of weight. Obese and overweight mean that your weight is greater than it should be for your health. Underweight means that it is lower than it should be for your health. Your healthy body weight depends on your sex and height. For children, it also depends on your age.
A sudden, unexpected change in weight can be a sign of a medical problem. Causes for sudden weight loss can include
Sudden weight gain can be due to medicines, thyroid problems, heart failure, and kidney disease.
Good nutrition and exercise can help in losing weight. Eating extra calories within a well-balanced diet and treating any underlying medical problems can help to add weight.