Welcome to the forum!
I am sorry to hear about your condition. Yes, it is perplexing. In absence of any other diagnosis, probably you should look at chronic fatigue syndrome or fibromyalgia. Graded exercise therapy is supposed to be beneficial in relieving the pain in such cases.
Deficiency of Vit D and
Vit B 6 & 12 should also be explored. Do discuss this with your doctor
Hope this helps. Please let me know if there is any thing else and
do keep me posted. Take care!