Hi Katy,
I have B12 deficiency caused by pernicious anaemia. Took me months to get diagnosed, but I know people who waited years for a diagnosis as GPs don't seem to acknowledge how bad it can make you feel.
I had 2 blood tests and was told both times, all results normal. When I went back a third time i asked for the actual results. I was told b12 level was 140, (minimum should be 200).
When I questioned the GP about this he said low b12 wouldn't give you symptoms like loss of balance, lethargy, fatigue, dizziness, palpitations, leg pains etc. Argued with him that it can as I have a strong family history of auto immune conditions and have seen others experience the same things.
Told GP I wanted further bloods done to check why b12 was low, as "low b12" isn't a diagnosis on its own.
He eventually agreed to do the tests and they showed I had pernicious anaemia. Was started on b12 injections the day results came back and haven't looked back since.
My advice would be:
Go to GP, explain your concerns and ask for blood test that will check b12 level.
When results come back ask for the actual number and don't just accept "everything looks normal".
If b12 is low you will need further blood tests to find out why , PA, coeliacs etc
Is there anyone you can take with you for support?
Feel free to send me a PM if you need any other info
Good Luck 