Very low levels of thyroid hormone usually indicate an autoimmune reaction to the thyroid gland itself. This means you’ll have to take thyroid hormone supplements orally, usually the stable form T4 (Levaxin), which your doctor can prescribe for you. Your body will transform this into the active T3 hormone when necessary. The supplement dose should be adjusted so that you reach normal hormone levels (TSH, T3, T4) and sufficiently alleviate symptoms – though a few people feel best when keeping TSH slightly below normal.
Then, when you weigh yourself, do it at the same time every day so you eliminate variables. (I weigh myself as soon as I get out of bed.) While you won't lose weight every day, you should notice a downward trend, and if you don't, you need to adjust accordingly. Look back on what you've eaten and how you've exercised and determine where you've gone wrong.
Here's something else most people probably don't know: Fidgeting is good for you. It's considered a nonexercise physical activity, and it's an important way to burn energy. You get more health benefits if, in addition to exercising, you are a more fidgety, more active person the rest of the day. This means gesturing while you're talking, tapping your foot, just moving around.