At my last checkup, all my vitamin levels were normal, or above normal, except for niacin and D3, which I now take in addition to my multivitamin.
A couple things; you should be taking roughly 500mg of B3 at the end of 2-3 meals per day. Build up to that amount.
And, you can’t absorb D if you’re low in mag and I’ll guarantee you’re low in mag.