serum b 12 tested today

[pinkypop]

i had severe migraines due to a wrong supplement and coincidently my b 12 levels were low

2014-180 pg/ml-neurologist put me on 6 shots of methylcobalamin, i took many more upto 17 shots

2016=3068 pg/ml b 12-after supplementing

stopped all b 12 supplements since , tested b 12 levels today

2018-oct-b12-227.5 pg/ml -again low

i was told 6 shots of methyl b 12 will last for 5 years ., but in two years it has reduced from 3000 to 200 pg/ml-is it normal to reduce so much in short span of 2 yrs ? will the active b 12 be low too ?any clarification would be much appreciated.