Meditate!!!
I am inclined towards the ADD mentality and for ages thought I had it. I read some stuff by Thom Hartmann which changed my mind. A similar attitude can be found on this site -
Attention Deficit Disorder♥ -♥ Born to Explore! . Although I don't know the severity of your situation I think the whole Hunter/Farmer paradigm is important -
Hunter vs. farmer theory - Wikipedia, the free encyclopedia.
Meditation has been the thing that really has allowed me to function mentally. It has totally allowed me to rise above the brain fog and gain some real clarity. It will be dificult at first but it is worth sticking with it for a few weeks so you really get the benefits.
I have also been using this -
The Worlds First Digital Drug (FLAC version) - The Pirate Bay) . It works really well for gaining some momentum with your meditation. I can be in a really brain foggy mood and listen to this and be clear minded. Make sure you get a flac or wav if you use binaurals because mp3s don't work apparently.
Good luck. You will get there. It is totally possible to fucntion better mentally and I am testement to that fact. Keep trying till you get there because something will work.