Hello I have gone throught your question and understood your concern. You should know that, most of patients with hyperthyroidism have the same problem as you. Due to the increased metabolism caused by the hyperthyroid condition, most people with hyperthyroidism lose a good amount of weight, and many of these people find it challenging to stop the weight loss. Some people with hyperthyroid conditions begin to gain weight when taking antithyroid medication,but some people do not gain weight even while on the medication.(like in your case) Your TSH level is not yet normal,this means that your thyroid condition is not totaly normalised and this is the first problem to resolve. The key of weight gain strategy is to normalize your thyroid hormone levels. Since the high thyroid hormone levels are usually responsible for the weight loss in hyperthyroid conditions you of course want to do what is necessary to normalize these levels. Here are my advices that may be helpful to gain weight in your circumstances: - Eat nutrient dense foods like meat,eggs,avocados, collard greens, kale, spinach, arugula, radishes, and carrots. -Consume one or two smoothies on a daily basis with some added protein. -Start doing some light at least 3 days per week .This can help greatly in gaining weight. I suggest to consult a dietologist if you want to follow a specific diet plan for gaining weight in your actual situation. Hope this information is helpful. If you have other questions,feel free and ask. Best regards.