I also do not know anything specific about
Digoxin, but understand it is, or acts similarly to, a beta blocker. If that is the case, it likely lowers you BP which could cause both dizziness and fatigue.
It has been my experience with BB, that it takes months to adjust. I take Metoprolol to lower my HR which is driven by AFib. It helps, and in the beginning gave me a case of too low BP, but that has mostly gone away... my BP is now near normal, again.