Due to various reasons (eg. age/bad diet/lack of exercise/etc.), i was suffering from brain fog, gut problems, low motivation/energy/fatigue, sleep problems etc. for the last couple of years. Finally, did some research, regularized my diet, disciplined my exercise and added the following supplements which solved all my problems.
1) Methylcobalamin (Vitamin B12) sublingual tablet. Important for vegetarians.
2) Multivitamins and Multiminerals (with optional ginseng etc.)
3) Omega 3, 6 and 9 (with optional gingko etc.)
4) Vitamin B complex with Zinc
5) Vitamin D with Calcium (500IU/500mg)
6) Vitamin C chewable tablet
Take only 1 of the above per day so that you rotate every 7th day. Finally; 7) Have a Pre and Probiotic capsule with lunch everyday to solve gut problems.
Note: If you are in India, you can get all of the above (and more) for low cost at any of the "Pradhan Mantri Bharatiya Janausadhi Kendra" shops in your neighbourhood - https://www.janaushadhi.gov.in/