Carol felt tired. She felt tired all the . She didn't use to feel tired. She used have a lot of energy. Why was she tired all the time? "You should eat more ," her friend told her. "Sugar will give you ." But Carol didn't want to eat more sugar. sugar would give her more weight. She didn't to put on weight. She wanted to have again. She finally decided to see a doctor. doctor told her that she had a thyroid . "What is a thyroid?" she asked her doctor. " can make you feel very tired. But don't , I can fix it," he told her.