Inability to concentrate and brain fog can be caused by a poor diet high in sugar and refined carbs. So eat whole food meals that are low in carbs and high in healthy saturated fats.

Stress is toxic to the brain, so try to relax.

Medical doctors receive very little training on nutrition and its effects on the brain and body. Drug companies that fund medical schools would rather have people hooked on their profitable drugs rather that to eat a healthy diet. It turns out that diet and nutrition play a much larger role than medical school training would suggest. So take some time to study nutrition.