AMB,
What I have learned is that sensitivity to hormonal changes or hormonal substitutes seems to vary widely by the individual. When I had surgery to remove a cancerous thyroid in 2015 (thyroid cancer is the only cancer treated exclusively by an endocrinologist and not an oncologist), I read the thyroid cancer message board, which is very similar to this one. There were many people on that board complaining that their doctors couldn't get their synthroid dosage right and they were excessively lethargic and drowsy or hyper. Some of these persons didn't have all of their thyroid removed as I did, and I suspect that they may have had vacillating weight issues as well (synthroid dosage is predicated entirely on body weight and adjusted based on TSH levels). I was really worried I would have the same issues but since my thyroid was removed, my dosage has only been adjusted slightly and when my TSH levels were off. I never felt anything unusual or abnormal when they were off the normal range.
So the metabolic reflection of hormonal changes may well vary. I should note that I once asked my PCP what would happen if I crash landed on a desert island and didn't have my synthroid. He told me I would die within 2 weeks and it would be a very, very unpleasant death before multiple organ shut down finally killed me.
Anyway I believe an endocrinologist can conduct tests which will potentially determine if something is off and potentially why it's off. In my case I am tested quarterly for TSH and thyroglobulin. I never did have a recurrence of the cancer and they would know if I did by virtue of a blood test. This was a good result because I was stage 3 with metastasis into 2 lymph nodes, which were removed.
My concern in posting here is that the J Pouch is blamed for something that is entirely different in origin. I have observed a tendency on this board to attribute causation of myriad issues to the J Pouch when it's likely the case that something else is going on. I urge you and anyone with these symptoms to consult an endocrinologist. My endocrinologist sends me emails on Yale Heath's network after every one of my quarterly blood tests and comments on the results. In 8 years on synthroid he has made 2 minor adjustments on my dosage. Other persons have their dosages changed constantly and can't seem to get it right. I maybe am lucky, or my system is adaptive. Not sure but things are good and never had hot flashes. I did have chills when I got Covid and they were horrible, so I sympathize and hope you can find a good answer and proper treatment.