After I have been feeling run down for months now they finally checked a few things and it was discovered that I have little or no testosterone (normal range 6-70, mine came back as <3, meaning 0,1, or 2, not measurable). My GP says that's probably why I feel so tired, unmotivated etc. Cortisol was also in the low range, as was estrogen, as expected. They did a vitamin B12 check that came back as excellent. He referred me to an endocrinologist.