500mcg of B12 is not very much orally.
Very little of that is absorbed, compared to your injections.

There is a connection with mental symptoms that does not
happen to everyone...
It is discussed here:
http://www.alternativementalhealth.c...s/pfeiffer.htm
It is controversial, but may happen rarely.

Are you taking methylfolate too? You might add that in 800mcg a day. They both work together and if you are not methylating due to DNA errors, you'd be missing the activated methylfolate.
It is called Metafolin by Solgar.

Rose, who used to post here, used to say there were ups and downs with replenishing B12. She was severely ill with low B12 and finally was diagnosed.

When do you take the B12? In the morning? By night it would probably be gone from your blood and into the tissues.

This study:
http://www.ncbi.nlm.nih.gov/pmc/arti...able/T1/#TF1-4
found that 500mcg orally led to 9mcg absorption.
Compared to an injection which gives 150mcg from a 1000mcg injection.
You can see a significant difference there.

I think it can be very difficult to figure what is going on. It could even be do to other medications you are taking.
My Lisinopril which I took at night, woke me up 2-3 hrs later with swelling and burning! (blood pressure medication). Some nights I'd sleep thru and some were a nightmare. (heart pounding was the worst).