If you notice that you’re gaining weight, without any changes in diet or physical activity, see a doctor. An unexplained weight gain could be a sign of hypothyroidism or underactive thyroid. It is a condition in which your thyroid gland doesn’t produce enough thyroid hormones that regulate many bodily functions, including metabolism. Without enough thyroid hormones, your metabolism slows down, and your body burns fewer calories, leading to weight gain.In addition to weight gain, underactive thyroid can cause symptoms like dry skin, muscle soreness, brittle hair, constant fatigue, frequent tiredness, poor appetite, menstrual problems, constipation, indigestion, increased sensitivity to cold, etc.If you have an underactive thyroid, it may be hard to lose weight. Bringing your thyroid hormones to normal levels is the first thing you should focus on when you’re suffering from hypothyroidism. So, consult your physician for thyroid medication. Here are a few certain lifestyle changes that can assist in your weight loss goal.