I am not a doctor, although I am wearing a lab coat and I have a stethoscope on.
Given the symptoms you describe, it is possible you may have a "low energy" disability like fibromyalgia or Lyme's disease, or maybe something else; who can tell?
>I< certainly can't!
But you need to look in for possible explanations for your weariness, and as your doctor, I suggest you get more time in the sun to boost your Vitamin D levels, and participate in a pleasant physical activity that gets your heart stimulated. But door-to-door work is specifically NOT indicated because it is both a "low energy" activity and a "high stress/low comfort" activity because you are required to dress like an insurance salesman at a funeral.
I want you wearing comfortable, loose-fitting clothing, STAT!
Just let the old boys back at the hall know that you've been diagnosed with "mumble-mumble" and will need to step down in the interest of your health. They CANNOT challenge you on this because your medical records are NONE OF THEIR DAMNED BUSINESS!
After you've dropped this bomb in their laps, make it immediately effective and don't go near the Kingdom Hall for any reason for at least six months - a year would be better.
They will forget about you, except on those occasions when they wish they had another sucker lined up to do some heavy lifting. Any time they "stop by" because of their "concern for you" tell them that YES, you are feeling better, but this is a long-term concern because, after all, you ARE still getting older in this "system" and the flesh is weak.
Try this, then take two aspirin and call me in the morning to let me know if you're feeling any better.