You might not only be low in norepinephrine. You might be low in ATP and GTP, which what I have discovered is most likely happening in people with ME/CFS. This low ATP/GTP will make norepinphrine useless since it will not trigger the production of cAMP, the secondary messenger of norepinphrine to do the things it needs to do to give us energy. Which is mainly to bring calcium into the cell. See the image below.
ATP and GTP are rugluated by Magnesium, which will rasie cAMP and cGMP levels, and zinc which will lower them.
We have a metabolic pathway in our body that makes noreipinephrine and there are many vitamin and mineral cofactors for the genes in that pathway, or genetic defects, that lower norepinepherine. Zinc, B6, Iron, Copper, Vitamin C are pretty much all of them. Genetic polymorphisms in any of those genes mean you might need more than the average person.
I am the opposite of you, I have too much ATP and GTP and taking zinc has reveresed all my symtoms.