Hi Clare,
Nice to hear from you.

The marked decline is indeed marked. Did you have a lot of stress to deal with? I think it's useful to get an idea of what might cause something like that.

Pernicious anemia is a condition where your body no longer makes or has intrinsic factor which is needed to use B12. It's pretty rare these days. Some B12 researchers theorize that lack of intrinsic factor is a condition that develops after a significant periood of low B12.

It is very common however to have other problems which lead to low B12 and those problems are commonly called B12 malabsorption illness.

Are you taking a multi with the other B vitamins? or a mega B to supply them?

The B vitamins really are a "complex" and need to be taken together. If not, then too much of one can cause a reaction in one of the others because it is low low in relation to the others... I realize that your overall B12 is low, but if your B12 test is in the 300s after all the injections... or did you only begin injecting after your blood was drawn for the test? it would appear to have been even very low at one point.

I have on my site an excellent article about how the low in Japan and some other countries is 550. So on that scale your B12 results would not have been normal in either month.