Being light headed, dizzy or heat intolerant can be caused by a number of things
What are you actual test results for Free T4, Free T3 and TSH? We're all different, so just because levels might be in the so-called "normal" range doesn't mean they're normal for you. Be sure to include reference ranges with lab results since ranges vary lab to lab and have to come from your own report(s).
Have you had a heart work up to make sure nothing is amiss with your heart since some heart problems can cause one to be light headed and dizzy, as well?