Being that the swelling is in one finger the first thing that comes to mind is possibly a spider bite or some other venom.
How long has this been going on?
As for the fatigue, this is common with diabetes. And you do not have to be overweight to have type 2 diabetes. A lack of chromium will close off insulin receptors. I recommend getting some chromium polynicotinate (not picolinate) 200mcg 3 times daily with meals.