It's important to keep in mind that correlation does not imply causation, or in other words, the new symptoms might not be related to the B12.

There could be other things playing. Sure, it is possible that you have an averse reaction to B12, but the chances are very very slim. If there is a relation, it might be that your body is readjusting to the availability of the vitamin, which can cause discomfort.

I've seen it established numerous times that people feel a bit worse when the B12 is kicking in before feeling better. ("initial worsening") I've also seen a lot of people getting stressed out by the injections.

Also, don't forget that even a hydroxocobalamin dose that is 10,000 times higher than what you are taken has been proven to not have dangerous side effects. (Obviously, don't try this at home!).

If you keep feeling worse, you might want to see if the reaction goes away if you stop taking B12. Needless to say I'm not a doc, and if things feel very wrong - you'll be the best judge of that - don't hesitate to contact a real one.