Hello Dear. Thyroid disease does cause weight gain. Generally hypothyroidism (deficiency of thyroid hormone) will cause weight gain. But there is loss of appetite, constipation, lethargy etc. Whereas in hyperthyroidism (excess thyroid hormone) there is anxiety, tremors, excessive appetite, and despite of appetite there is weight loss. So im not able to exactly point out where your symptoms fall into. But definitely a blood test for thyroid function tests will reveal you, whether you are having hypothyroidism or hyperthyroidism. But your weight gain in short period of time is surely due to your thyroid disorder. I suggest you to take medications regularly as prescribed by the doctor. Go for morning walk. Do regular physical exercise. Cut down on bad habits like smoking, alcohol etc if any. Hope i have answered your question. Feel free to contact me if you have any more questions. I ll be glad to help you. All the best With warm regards Dr Sanjay Kini