Hello, I understand your concern. Feeling constantly tired at such a young age and with a lifestyle requiring a lot of energy, can be very frustrating. One reason for low energy and tiredness when on medication is usually the low T3 level. As you may know, T3 and T4 are forms of the thyroid hormone, where T4 is the storage form and it has to be converted to T3 in order to be picked up and used by the cells. Sometimes, there is not enough T3 to supply the cells quickly when needed because in some people the conversion from T4 to T3 happens at a slower rate, hence the low energy. One solution to this is taking a direct source of T3, which is usually made of desiccated porcine thyroid, such as Armour thyroid, so I am assuming this is the reason your doctor decided to switch you from synthroid. Since you are not feeling better on this new medication, I strongly recommend, if you haven t already, to do some blood tests to check for blood sugar levels, adrenal gland hormone levels (the dysfunction of this gland could also be a major cause for your tiredness),and your iron levels. In the meantime, taking a multivitamin supplement, as well as a B12 vitamin supplement would make quite a difference in your energy levels. Exercise is not recommended in your case, and alternatives such as yoga and tai chi can be the appropriate type of exercise your body needs to find a balance. Also, needless to say, managing the right kind of diet, with no gluten and plenty of fruit, vegetables and protein, as well as enough sleep, are vital lifestyle habits you need to acquire and maintain for life. Wishing you good health and all the best.