I tried the thyroid theory for my fatigue actually and it didn't help. It was something else but still the same idea. It was a 'wetware' problem (really effed up gut microbiome that needed to be whacked and restarted with good bacteria and feeding them the right food).
You can see it in other posts from me. I think the histamine intolerance part was fixed by the Bacillus subtilis that's in what I take. Though some of the regular lacto bacillus strains certainly helped crowd out whatever was in me before. But some lactk Bacillus actually create histamine. For exame I could not drink Actimel.i can attest to the fact that it has live bacteria that make it to the gut alive because actimel gives me headaches (literal headaches not figure of speach)
I started with 1 a day and worked up to 3 a day over some weeks. I felt like crap for about 2 weeks. Like having a cold sick. Just no nose running and such. Then better than ever. Now I take one in the morning and one in the evening.
Oh and so I don't forget shortly after I also started keto. Real keto w/ less than 20g carbs. Did blood tests that confirmed I was in ketosis. That's the "and feeding them right" part. Did it for about a year which normalized all my off blood markers except for cholesterol which also improved but not below what is condered normal. Did it for a year. Now I no longer do keto but keep the sugar mostly away.
By way of analogy, imagine that you have a crippling fatigue due to low thyroid activity, and not knowing about the underlying issue you try to fix the fatigue by a rigorous exercise and rest regime. The progress will be painfully slow and often reversed. Alternatively you can get the thyroid pill and become a normally functioning human without the super-human effort.