Welcome to NeuroTalk:

I have a few short questions:

1) Did you have a B12 test done before starting your supplement?
Is it the cyanocobalamin or the active methylcobalamin?
Do you take it on an empty stomach?
Some people lack the genetic enzyme to convert cyano to active methyl. If this is you and you are low to begin with, you won't see much or any benefit from what you take. It should be taken on an empty stomach as very little is absorbed, and that little bit which is all you really need, can be lost when food is present and never get to the places in the small intestine where absorption exists.

2) Is the magnesium in your supplement magnesium oxide?
If so you will have to take another form because it is not absorbed. Another chelated type like citrate, gluconate, lactate, or malate, etc are alternatives. Eating almonds, beans, and yogurt, may help as they provide good amounts as food sources.

3) watch your calcium intake when taking that high dose D3.
Some cardiologists are suggesting that with high dose Vit D3, much of the calcium in foods is more absorbed, and supplements should only be done in much smaller doses if at all.

4) Essential fatty acids, like fish oil, need to be taken every day, if you are not eating good food sources. Our bodies cannot make them, and they must come from food or supplements. Your dry skin may reflect this need. Make sure you take at least 3 a day with food. You can break that up as one with each meal, which makes them easier on the stomach.