Metformin is nasty. Even just on a single 500 mg dose in the evening, In addition to fatigue and constant headaches, I had horrible stomach upsets all day, every day for over two months before I gave up. Metformin is often the first treatment given because it is very cheap and practitioners just prescribe it out of habit. If you are still having difficulty tolerating it, work with your medical team to find a better alternative for you.