Fogginess in brain. Kindly, help me.

I am 24 yrs old student. I am suffering from fogginess like feeling from past three years in my brain. The feeling came at the end of 2015.  Fogginess, initially was only in my front portion of my brain, behind forehead and then expanded to whole brain. In November 2016, someone told me that it might be depression. So I undergo the depression treatment for almost two years, it helped me to some extend. But I still feel a minor fog in front portion which is enough to spoil my daily activities. I feel so dull, poor memory and this fog acts as a big obstacle in focussing on something. I can't focus even for 10 seconds while reading. I have tried everything thing to know, what exactly I am going through. What is the name of this disease. But everything went into vain. Kindly, help me.