I have similar symptoms of fatigue, poor concentration and trouble staying awake as you. Doctors have done all tests including for vitamin D, Iron, and Thyroid. Everything seems normal. And I did feel that grapefruit seed extract helps me with the brain fog. I also have a burning tongue after eating. No other symptoms. Did you have any other symptoms of Candida or just fatigue and brain fog ? Also, did taking grapefruit seed help you ?