Weight loss is a classic symptom of overactive thyroid - unfortunately, I never had that symptom!!!
If you had a mild or early thyroid problem when they checked you, it might not have shown up before - there is a normal "range", and if normal for you is at the low end of the range, and you move to the high end of the range, you could be high for you but still have "normal" test results. Make sure they have done a TSH, and ask for your results. If thyroid disease runs in your family, also ask them to check you for thyroid antibodies.
