Thyroid hormone T3 is what gets the job done and fT3 should be tested. fT3 regulates body temperature by regulating mitochondrial metabolic rates. Mitochondria product ATP, the universal currency of cellular energy. Body temperatures are a very important indicator.
We have histories of guys here who have had lower body temps who were iodine deficient who improved energy levels and body temperatures by taking iodine. If someone does need Rx thyroid meds, great improvements are achieved.
I did ask you to read thyroid basics explained in one of your other threads and also asked about your intake of iodized salt.
If you keep spreading your history across multiple threads, you will not get the best assistance.
Doctors are not very expert at these things and never seem to really want to understand the issues. Iodine deficiency is quite common and I have never seen a report of a doctor asking about iodized salt intake. They will tell people with high blood pressure to not use salt and then they induce iodine deficiencies. Do not take doctors as authoritative in any of this.