EC -
Some ideas for this:
+ Heat intolerance at your age very well could be due to low B vitamin and methylation status. In particular, thiamine (B1) is a root cause.
+ Low Vitamin D is another driver.
+ Hyperthyroid would be the other angle. However, I doubt you had that issue at 33.
Potential Fixes:
+ Eat Grassfed Liver - Either 1oz a day or 4oz twice a week. (US Wellness Meats)
+ Take Methyl- B vitamins (Amazon) (if you can't eat liver and/or on days you don't)
+ Take extra B1 from a high quality supplement like Thiamax
+ Take 5000-10000IUs of a vitamin d3/k2 liquid. (Thorne is good)
+ Check Thyroid status with the old fashion way (Thermometer under arm) after a month if you decide to try this
https://dannyroddy.substack.com/p/demystifying-thyroid-supplementation
All of these recommendations should help energy with many more thing beyond heat intolerance as well.
Nutritional Therapy is far better than Medication Therapy. Your body knows what to do with nutrition.
*Not medical advice.