I agree that reducing the intensity of your work outs -- keeping them routine -- may give you a better idea about the source of the exhaustion. If it's the exercise, then a less rigorous workout theoretically should reduce the exhaustion.

I'm one of those people for whom physical exercise has but a minimal, fleeting effect on my depression. A long-term dedicated exercise regimen failed to keep me from crashing in the 1990s. I believe my experience is anomalous, though. Exercise should help, or at least support your other mental hygiene efforts.

Success and all the best, Googley!