I was kind of skeptical about the whole "let HN play Dr. House", but I have to admit the symptoms on the wikipedia page seem to match the OP's symptoms very well.
Even if he/she doesn't have Pernicious Anemia, it's a really good suggestion.
It's probably not the best idea to have a bunch of non-doctors randomly scanning Wikipedia's medical pages trying to backfit lists of symptoms they have no personal experience with to the OP's described condition.
But it is probably worth exploiting the odds that someone out on the Internet has experienced the exact same difficult-to-diagnose medical problem, eventually figured it out, and lived to help others do the same.
If your doctor won't give you a B12 shot tell him to shove it up his ass, and get a new doctor. It's not like you're asking him to write you a 'script for 300 oxycotin tabs.
The control-freakish nature of many medical professionals astounds me.
Anyway, you can also try large dosage (5000 mcg) sub-lingual B12. Some of it will make it into your bloodstream without going through your stomach.
Second this, about a thousand times. I don't care where you live, there is somebody in town who will give you a B12 shot. Drop your current doctor, and be sure to write him a letter telling him why. You might save somebody else.
PS - Keep in mind that B12 can have some side effects:
Hematologic: Peripheral vascular thrombosis has been reported. Treatment of vitamin B12 deficiency can unmask polycythemia vera, which is characterized by an increase in blood volume and the number of red blood cells. The correction of megaloblastic anemia with vitamin B12 can result in fatal hypokalemia and gout in susceptible individuals, and it can obscure folate deficiency in megaloblastic anemia. Caution is warranted.
Leber's disease: Vitamin B12 in the form of cyanocobalamin is contraindicated in early Leber's disease, which is hereditary optic nerve atrophy. Cyanocobalamin can cause severe and swift optic atrophy, but other forms of vitamin B12 are available.[citation needed] However, the sources of this statement are not clear, while an opposing view[45] concludes: "The clinical picture of optic neuropathy associated with vitamin B12 deficiency shows similarity to that of Leber's disease optic neuropathy. Both involve the nerve fibres of the papillomacular bundle. The present case reports suggest that optic neuropathy in patients carrying a primary LHON mtDNA mutation may be precipitated by vitamin B12 deficiency. Therefore, known carriers should take care to have an adequate dietary intake of vitamin B12 and malabsorption syndromes like those occurring in familial pernicious anaemia or after gastric surgery should be excluded."
Those are rare but worth being aware of. My friend has been taking bi-weekly B12 injections for over 2 years now with no problems, and it continues to completely suppress the PA symptoms.
If your doctor won't prescribe them, find a new doctor. You need a doctor who is going to work with you in this situation.
I've been in a similar situation myself. Having a doctor I could sit down with and say "OK, here's my latest research, can we try this?" was critical to both my physical and mental wellbeing.
Unfortunately (or fortunately, depending on your viewpoint), it became my job to find out what was wrong with me and his job to make sure I didn't hurt myself in that process. I have a very different view of the medical industry as a result.
This is exactly what I've been doing for 18 years. Hiring and firing new doctors, and trying to navigate "what should I investigate next?" on my own. To be fair, there were several doctors who were willing to try (just about) anything I brought to the table, and when they were all out of ideas, they admitted as much. Unfortunately this type of doctor is rare, in my experience. Which is why I'm asking for help finding a good one in my area (Cleveland).
FYI, I dug up an email from my close relative who had this.
Her levels at the time she had the condition were: B12 at 328 pg/ml and folic acid was 15.1. She said that that was considered on the low end of normal (which is why it went undetected for so long). After the shots, the B12 levels have been in the 600 range. Like most anything biological, B12 levels can affect everyone differently.
While your waiting for a B12 shot, you might try taking some sublingually with sorbitol. The latter allows most (but not all) people who have absorption problems to get enough.
Even if he/she doesn't have Pernicious Anemia, it's a really good suggestion.