Hi. My 20 Year Old Daughter Has Had A Weight

Hi. My 20 year old daughter has had a weight issue for the past 2 years. She is very active and eats extremely healthy and small portions. But gains weight non the less. I took her to neuticionist to endocrinologist and have no answers. One dr put her on cytomel 5 mg small dose for low t3 t4. But he was the only one who thought she is low. A month later nothing has changed. She is still gaining weight. What should I check for next? I'm all out of ideas.