Why Do I Feel Excessively Cold And Experience Constipation And Weight Gain Despite A Balanced Diet, Especially Since I M On Synthroid For Hypothyroidism?

I feel colder than others and the degree of cold varies by the minute. I wear anywhere from a T-shirt to three down jackets within an hour. I am also constipated and gained weight that I can t lose despite a low-calorie, balanced diet. I am 65, on Synthroid due to hypothyroid.