Unrelenting brain fog and cognitive issues

I've been searching for months trying to find an answer to my non-stop brain fog and cognitive issues (memory problems, communication issues, can't think straight) and I haven't found an answer yet. It's really concerning me as I seem to be getting worse every few weeks to the point I had to leave my job and can't drive a car.

The reason I'm posting here is because I think there's a supplement that may be able to help me based on the following: I had a tiny bit of improvement a few weeks ago, it was short lived, but the day prior I had a Vitamin B1 supplement. Also, my test result for Vitamin C came back very low.

A quick bit of background is that my vitamin and nutrient panels have came back fine (b1, b2, b6, b12, vitamin d), my thyroid is fine (extensively tested), my brain scan is fine, blood glucose is good. Other symptoms also include dizziness, fatigue, some burning in fingers and toes as well as some "chicken skin" rashes.

The connection between improvement and B1 is just a guess, as I've tried again and again to repeat it without luck. I took 250mg of Thiamine nitrate the day before I saw a few hours of improvement. It could also be coincidence.

I have also experimented with liposomal glutathione, activated charcoal, and other detoxing agents with no effect.

My Vitamin C level was 2 umol/L. I don't think that would cause all of these neurological symptoms though? (is it urgent to fix this btw, or should I slowly supplement?)

Does anyone have any suggestions?