As trucker suggested, see a doctor first, I can tell you that it took me over a month sober before the fog even began to lift, but for me it did, I do recall that as with anything it does take time.
Some things that will help is taking a multivitam and a B complex daily, eating right & getting PLENTY of liquids.
If after seeing your doctor he gives you a clean bill of health, then just give it all time, it does get better the longer you stay sober.