Have you looked into what you're eating and doing for exercise? You definitely cant power through brainfog with caffeine anymore.
try the following to get yourself back on track 1. first meal of the day should be a filet of fatty fish like salmon with skin. if you can't afford this, use a high quality fish oil pill like nordic naturals. keep it refrigerated. omega3 fatty acids are prone to oxidation at roon temperature and there are no official stadards for it in america)
2. limit carbs to whole foods like sweet potatoes, yucca, potatos
3. cut out all sugar outside of whole unprocessed fruit. (juice doesn't count)
4. have a side of greens with each meal
5. start lifting weights, (triggers release of HGH)
6. choose one day per week to do a 24 hour fast.
after 2 weeks, you'll start to feel your brain come back