I think that 690 is suspect, altho it does fall in the low-normal range.
B12 supplement wouldn't hurt, and you might benefit from it.
You cannot overdose on B12- excess is excreted, just like vit C.
In the Methyl form (methylcobalamin) as opposed to cyanocobalamin,
it is more readily absorbed by the body.
I take 1000-2000 mcg (1-2 mg)of methylcobalamin per day, sublingual.
It has brought me up to 1100-1200 when last tested.
I've been taking it daily for over 7 years.
I get Jarrow brand form iherb- it is fairly inexpensive, if you get a 3 or 4 mo supply.