In most cases it is best to add things one at a time. You could try dropping the adb12 for now and adding the hydroxy if you want. The hydroxy is converted into adb12 by the body, though your ability to that is somewhat impaired. It should help the methyl cycle along better too. Adb12 has to do with energy production and isnt converted to mb12. Hydroxyb12 is the precursor to both.
I wonder if you might be having problems with your lower esophageal sphincter and what could be causing that. If the problem tends to track alongside your overall level of inflammation, its probably not that. An inflamed gut that isnt digesting food can cause heartburn. Inflammation in that area can cause problems with that valve too, as can too much acid. Are you taking anything that is mucolytic?
Many people with cfs or chronic infections go through a phase in which they get pretty sick before they get better. If your body was infected with who knows what and wasnt fighting it, your gonna feel it when it starts to. Its a possibility. As long as it doesnt become chronic (lasts longer than 2 or 3 weeks) then it might not be a bad thing. This is of course if the increase in symptoms is due to the vitamins and not just randomly getting sick, and is still only one possible scenario.