Al Klein, I have little experience in this area as I've only just learned about methylation recently.
With that being said, regarding the sublingual, I am wondering if you might be reacting to a substance in the product other than the B12 itself.
So many of the methylcobalamin sublinguals have ingredients that can cause irritation or even wear away tooth enamel, such as citric acid.
Besides avoiding holding acids in my mouth (as advised by my dentist because my tooth enamel is fragile), I try to avoid artificial sweeteners, flavorings, and colorings where possible, and most methyl sublinguals have those too.
Of all the methyl B12 options, I chose Natural Factors sublinguals, because all they have in them are: lactose, cellulose, croscarmellose sodium, magnesium stearate. I got the 1000 mcg and they also have 5000 mcg.
Note that in those doses, Natural Factors seems to have two forms of methylcobalamin for sale, and the other form has the more traditional flavorings and artificial sweeteners, so one must be observant when ordering.
[If you are a follower of Freddd's protocol, from what I could tell in my research, it seems that he rated the Natural Factors methylB12 a 3-star or 4-star, meaning he
did feel effects from it, but it wasn't in his top 5-star level -- which now only contains one product.]
Since ordering the methyl form of B12, which I did before I got my genetic tests back, I have received my results and found out that I am compound heterozygous for the main 2 MTHFR mutations, and apparently people with my SNPs are meant to use hydroxocobalamin instead of methylcobalamin.
Therefore, I recently ordered Perque hydroxocobalamin. It contains mannitol, succanat, magnesium, and cherry fruit extract. I am not thrilled with the natural and artificial sweeteners in that, but at least there is no citric acid in it.
So, before giving up entirely on sublingual methylcobalamin, you might want to try the gentle Natural Factors one, or maybe give the Perque hydroxocobalamin a shot.