Omega 3 and 6 oils are very good for brain function and health.Fish oil can help depression,I find eating smoked salmon a little slice a day with my toast at breakfast helps a lot.
I can get it quite cheaply in the UK at ASDA(Walmart)supermarket.It is worth a try.
Vitamin D3 is very important,and a deficiency causes extreme tiredness and you can feel very ill indeed.