If it makes you feel any better, nobody's health problems are usually easy to diagnose or treat. I have a fabulous doctor who practice natural therapies, who is willing to prescribe supplements and do things other MD's won't, and who has confirmed through tests a lot of things I already suspected, but frankly, most of the real healing I've ever done has been due to my own experimentation and research. Patience and proactivity are keys to managing your health yourself, especially if you can't find a good doctor to be your partner in your journey. I'm lucky to have one, but I know not everyone is.
Irritation of the epithelial tissue of the mouth can be a start-up reaction from mB12. I had it a little bit, and I've read others have had it, as well.
The burning in your feet is another symptom start-up symptom I've read about. I don't have any neuropathy symptoms but a lot of other people do. Freddd had a terrible time with them. For most, mB12 seems to start waking things up, with a gradual lessening of symptoms over time.
I take injectable mB12 (2 -5 mg in the a.m.) plus 10,000-20,000mcg sublingual spread throughout the rest of the day. I usually put a 5000mcg tab in right before I go to bed, to go along with my last bit of folate for the day. Folate needs mB12 to work so I always take a bit of mB12 when I take folate (divided doses 3x/day).
FYI, there is always some "gunk" in my gums from the Country Life mB12 when I wake in the a.m. I suspect the gunk is just a fact of life if you're going down this road.
I've had ups & downs with the mB12 dose (I went through a period where it made me a little spacey, another period where it made me sleepy in the middle of the day, etc.), but things have stabilized now. I'm actually taking such big doses because I want to see if it has a beneficial effect on my hearing loss.
I take between 2500 - 5000mcg of adb12 (Anabol Naturals). Depends on how much comes out of the capsule when I open it in the a.m. LOL The adb12 gave me a lot of energy right off the bat so you may want to start pretty low with that until you see how you react. I loved it, but it can help create jitters/nervousness/insomnia if you take too much. I took too much initially and had to back down for a while. Now I'm stable and it feels good. I always take it first thing in the a.m. because I still think it could affect my sleep. If I forget to take it in the a.m. (not often but it happens occasionally) I'll skip it for that day. Adb12 gets stored in the mitochondria so once you've made up a deficiency skipping a day here and there won't matter. MB12 is different, because it clears the body fairly rapidly. This is why you have to keep dosing throughout the day to keep blood levels relatively high.
I also take active form of B6 (P-5-P), active form of B2 (riboflavin 5-phosphate), active form of thiamine/B1 (Benfotiamin), and every few days the active form of pantothenic acid/B5 (panthenine). The doses of these individual vitamins are appropriate for keeping things in balance, so I take them daily, except for the panthenine. It's a huge dose so I don't take it every day. I could split each capsule into more capsules but I'm lazy. LOL I do try to stay alert to changes so if something goes out of balance I won't let it get to far.
It all takes time, so don't expect miracles overnight. And if you do experience a few days of a miracle (you wake up going "I FEEL GRRRRRRREAAAAT!!!" or similar), don't be upset or surprised if you have a setback. It's happened to a lot of people. It happened to me. When I first started Freddd's "Deadlock Quartet" I had a great couple of weeks and then boom! Sick, sick, sick. I had to take a whole week off work. So I researched some more, adjusted my doses, added some things, subtracted some things, lived with the side effects, adjusted some more. It's a whole process. Still processing, in fact. But I'm much better off than I was before I started all this. I hope it can be the same with you.