You might try an axial body temperature study. Low cortisol can cause you to have many of the symptoms of hypothyroidism, with absolutely normal thyroid homone values. Below normal body temperature can make weight loss extremely difficult.
If you have adrenal fatigue, you are probably excercising less. You may not even be aware of it. Even a small reduction in exercise over a period of time can result in substantial weight gain. Cutting out even 100 calories worth of exercise each day will result in a little less than a pound of weight gain each month.