Some people such as myself have a genetic predisposition/sensitivity to depression and other mental health problems, including anxiety, brain fog, irritability and so on.
My own depression/anxiety/brain fog was cured through dietary means, and in particular with the use of targeted quality supplemental nutrients.
I follow the Nutritarian lifestyle/diet as a basis for improving cellular health and which has its origins within Natural Hygiene............ http://www.drfuhrman.com/library/are-you-a-nutritarian.aspx
If you take a holistic approach to your health, and include not only diet but exercise, fresh air, sunlight exposure, adequate rest and sleep, and as your body calls for, then you will be rewarded with superb bodily and mental health given sufficient time.
Nature works very slowly.