I do understand that you are on thyroxine
replacement since your thyroid
gland was removed. The dose of thyroxine is usually adjusted to maintain your TSH to normal. If your TSH is normal then it implies your thyroxine dose is adequate and weight gain is not related to thyroid. Weight reduction requires regular diet and exercise. There are also medications for weight loss
and your endocrinologist
can definitely help you in this regard.