I had a total thyroidectomy and have gained 20 pounds despite being in a pharmaceutical hyperthyroidism state to treat papillary carcinoma.?

It is likely from Fo. It is likely due to excess of calorie intake. Low thyroid levels do not cause this kind of rapid weight gain. You need to start cutting on your Food/calories consumed and begin to do some daily exercise. Start with a daily walk for 20-30 minutes and eat mostly plant based foods and cut down on meats, dairy products and all fast foods and foods with high sugar content. Aim for losing 1 pound/wk.