Blood test should show you if you have vitamin deficiency, imho it's much easier then diagnosing yourself.
In regards to B12 I've read somewhere ( when I'll find this link I will post it) that food containing B12 has to be consumed in smaller amounts, but frequently for the better absorption of vitamin. This is because there is a limit of how much of B12 an organism can absorb in one go. That's one of the reasons why eating once a week even one month's supply of the vitamin would be less efficient then having just a minute amount of it in food few times a day. Once again if you are not hungry it won't do you much good eating a kilo of sausages in regards to B12, your body won't take in the same percentage it would absorb if your're hungry or after some fasting.
I don't trust supplements or taking vitamins on the side, because of the controversy on the subject and just my own common sense, but I won't delve into it any further.
*Edit* Probably you know , but anyway, to absorb B12 properly organism has to get decent amounts of vitamin D. Just a footnote.
I don't eat meat, but I eat fish. Quite a lot of it is of oily variety like herring or mackerel, and wild salmon occasionally. Sometimes I consume quite a lot of it, so I became a little concerned about mercury levels. There is a mercury calculator in fish to give one an idea and keep within limits. If anyone's interested here's the link
http://www.gotmercury.org/article.php?list=type&type=75
Anyway to counteract mercury intake I eat quite a lot of coriander, it almost became my salad (leaves) substitute. It supposedly removes heavy metals and toxins from the body and the brain.
Water, I distill it, and use it for drinking and general cooking purposes.
There is cooking utensils problem as well, like metal and what not leakage into food during the cooking process.
One older gentleman started me in this direction, his organism reacting sensitively to iron, stainless steel, not to mention those non stick surfaces. The only surface he claims he can tolerate so far for cooking is the stone one. I agree with him about the food, that all the poison is targeted at young and strong and therefore unsuspecting people.