Vitamin D deficiency is very common. I had it. It's good to get your D tested twice a year
If you were taking anything with B12 in it within 4 months prior to being tested, your results will be higher then they actually are.
Levels should be above 500, closer to 1,000
You can have symptoms at a cellular level even at higher levels.
2500 a week isn't much. B12 is water soluble.
Only about 10% will be absorbed in your body and that's if you don't have gut issues that can prevent absorption.
I took daily higher amounts of B12 lozenges (that dissolve under my tongue) for a few months, then dropped it to 5,000mcg. Methyl Folate (B9 folic acid) will help the B12 be utilized in your body.
Yes it could be Vitamin D deficiency. Have you gotten blood work?
Low magnesium, Vitamin B12 & ferritin can also cause your symptoms