Hi Vickie,
I wonder if your B12 deficiency is causing depression.
Being profoundly exhausted (and having your symptoms dismissed by ignorant people, who don't understand how damaging B12 deficiency can be) would be easily enough to cause depression.
My B12 deficiency made me exhaused, exasperated and very, very cross. The difference is probably a question of our underlying personalities. It was useful when I had to power my way through the red tape of my GP's surgery to get to some decent treatment. I wish I could lend you a bit of my "ggggrrrrrrrrrr"! : )
It sounds like the treatment you are receiving isn't hitting the spot. Go back to your GP and ask for blood testing to determine your present B12 and Folate levels, plus your Haemoglobin, Red Cell and Ferritin levels. It wouldn't hurt to have a full spectrum, to make sure there's nothing else wrong.
Ask for a printout, and do your own research into what levels should be online. Low iron may be fixable with tablets - cheap as chips. Low folate will mean you can't re-cycle B12, and must also be addressed. Low B12 causes knock-on deficiencies in other vitamins.
Explain - firmly - to your GP that you are still not feeling well, and that this is making you withdrawn. Lay it on thick. Tell them that, internationally, a minimum B12 reading of 500 is standard, and that over 700 desireable. Do not accept the present NHS nonsense about 190. If quarterly jabs won't achieve this, go to monthly (that's what I get, on the NHS). If that doesn't do it, then you should be looking for other causes of your anaemia, like bleeding in the bowel. You need iron tablets as well as B12 jabs if your iron is low.
If you still don't get better, then your GP should be looking at different formulations of the injected B12 (Cobalamine) which you may absorb more readily.
Depression COULD be an early sign of neurological damage, and left long enough, it will be permanent. Currently, it is generally felt that B12 deficiency may have a significant part to play in the development of senile dementia.
Gather yourself, grab this problem by the throat and shake it hard. It can easily be subdued. : ) Chin up.