Are you on thyroid medication? Is it low or just subnormal. If you have been put on medication, you will definitely lose weight and have increased energy just from that alone. If it is not low enough to be put on medication, you may have low energy levels and have a lot easier time gaining weight. Even if you are tired, exercising, and chasing after three little ones probably gives you a lot of that. Cardio-exercise will increase your energy level and help you burn calories. Following a low cal, low fat diet would also increase your energy and help you lose weight.