Hi mate, welcome to BL.
Whether you lose weight depends on what you eat, and how much exercise you do. The ephedrine might give you a boost for a while, but without those other things getting sorted, your metabolism will just adjust to it, you'll probably eat more, and eventually you'll regain the weight.
What does your diet look like? How much exercise are you doing?
Also you say you have an underactive thryoid - is this an official diagnosis? Is it being treated?