15 years ago my daughter's health was going downhill. Constant chest infections, always sleeping and losing weight. Because of my knowledge of the thyroid, I suggested she see her university GP and ask for thyroid blood tests, which he did carry out, but as in so many cases, the results came back within range. On the way out, he told her, 'don't be stupid, you'd be fat if you were hypothyroid!'
We finally had her diagnosed on clinical symptoms by a private consultant and she never looked back. She was on thyroxine first of all, but when she changed to Armour thyroid, she regained her health and her weight. The adrenal glands play so much of a part in thyroid disease.
I can't put my hands on the appropriate medical papers at the moment, but I am sure if you type into the search engine something like hypothyroidism and weight loss, you will actually come up with evidence to show your doctor.