Insanely low stamina can be from depression. Emotional apathy can be from depression. Or, if severe, it could be anhedonia. Anhedonia can be from a severe depression, but can also be a manifestation of schizophrenia (look up "negative" symptoms of schizophrenia and see if they ring a bell; schizophrenia usually debuts in adolescent period).

Or it could be a deficiency of testosterone. Or, a multitude of other things. Maybe you need hormonal injections. At any rate, you need a very thorough physical with a full workup of tests and a thorough psychiatric eval, and - this is key - you need the person doing the medical assessment to talk with whoever does the mental health eval. They have to talk to and update one another.

This is probably an urgent concern, because there might be a certain window of time past which interventions won't help.