Constant brain fog

Hi all, looking for some advice:

Since early 2014 have been experiencing daily brain fog - lack of concentration, awful STM, irritability, difficulty problem solving etc. Current additional symptoms include mild visual snow and 'blurred'/slowed vision (have had eyetest and no issues there), fatigue, premature greying, constant tingling soles of feet and often cold hands. It came out of nowhere, with onset I felt a bit duller for 2 days then on the 3rd felt like was going to pass out, didn't, but have been suffering since.

After 1 week symptoms vanished, had about a week of normality then symptoms came back and have stayed ever since.

Other symptoms have come and gone, all cleared up by Oct 14:

-Headaches, esp. around eyes.
-Nausea after food, pulsating around stomach & extreme light headedness - never vomitted, just gas.
-Twitching eyelid
-Mild social anxiety

At present, symptoms i'm dealing with are chronic brain fog, fatigue, prem greying, irritability and inability to handle stress, cold hands, visual snow and tingling feet.

Blood work & urine analysis at docs after onset came back with a mild Vit D deficiency, and serum potassium and MCH a touch over high end of range. Other than that, TSH quite high at 3.5 but within their range (up to 4.50)and had free T4 at 14.8. Have seen 4 diff. docs and all lean towards mood/ Depression issues which just isn't the case. Depression is one thing i'm surprised I haven't got!

2 things i'm considering are Iodine deficiency (although 12% Lugol's generously applied disappeared between 17 - 24 hrs whilst asleep, not particularly quickly), and candida - candida spit test flags up and also often have white on tongue.

Any thoughts/suggestions would be greatly appreciated