Mood shifts are also common with thyroid problems. A lot of dr's test thyroid before they prescribe antidepressents or other bipolar meds to rule out thyroid problems first as mood problems are a common symptom of thyroid troubles. And thyroid is treatable . I'd say it is good if they can pin your issues down to one cause. Better than trying to treat multiple illnesses or trying to treat only symptoms without knowing the root of them and treating the actual problem.

If it is thyroid I doubt they would only try to fix your weight. I have know many people both with hypo and hyperthyroidism and treatment focuses on correcting thyroid function.

Hopefully they will have an answer for you.