It sounds to me like what you had accidently fallen into wasn't so much flexetarianism, but maybe more like an extreme version of vegetarianism, but in such a way that it wasn't obvious that that is what was happening. So you couldn't prepare for it by researching what you might need to stay healthy.

I have heard of at least one supplement marketed to vegans that contains only b12 and b6, so someone somewhere recognizes that extra b6 is important when our meat consumption drops to zero.

I think there is a big difference between zero and moderation (2 or 3 ounces per day). I think of myself as a person who struggles with moderation, and I know I tend to take things to extremes. What I've realized lately is that almost everyone can fall into this kind of trap.

We end up eating too much of something (added sugar in all of our foods and drinks, more meat than is really good for us) or go to the other extremes of zero meat or 'low-carb' diets, both of which can be harmful in their own way.