Finasteride can act as a corticosteroid, thereby suppressing the immune system, which can make you more susceptible to serious infections. People on immunosuppressants can get serious infections (tuberculosis, HIV, cancer, etc.).
Now, it is also possible, however, that we were all infected PRIOR to finasteride, and taking fin basically suppressed our innate immune system from curing us or keeping those pathogens in check. For example, I have Epstein Barr virus (mono). many people with EBV ALSO have chronic fatigue. Perhaps fin sort of allows EBV to take hold.
Low vitamin–D is correlated with infection and inflammation as well as autoimmune disease. It is also possible finasteride modulated the immune system to trigger an autoimmune disease. However, many also believe autoimmune diseases are in fact bacterial (i.e. pathogenic).
So, this chronic infection theory is quite good. And the solution may be to ramp up the innate immune system. Some possible mechanisms of doing so would be to increase glutathione levels and to reduce vitamin D (well, according to Marshall Protocol since Vit D acts as immunosuppressant it would be the last thing we want). This might make us feel worse initially btw. I think a poster on here said glutathione made him feel horrible. But it is possible that it is actually curing us.