Thank you for your query,
As your child is having frequent headaches
, excessive tiredness
, increased body temperature and sweating even in cold temperature these symptoms may occur with thyroid abnormality and mostly it is due to hyper function thyroid.
You told child blood for thyroid function test is abnormal so mostly it is suggestive of hyperthyroidism
So consult Pediatrician
with the thyroid reports and he will guide you properly.