What causes b12 levels drop rapidly in may it was 100 after injections in june 600 again today its 140 how sudden drop m waiting for reports of intrinsic factor?

Vitamin B 12 : My guess is that your body has been putting the injection to use. The level in June was because of the injection, but, your body processed and stored that supply, and you probably just need a few more injections. B12 is a micro nutrient, you don't need much of it, and once your stores are complete, your level should stay normal four months to years.

Low stores: You likely have very B12 stores and right after the injections get high levels, but once the B12 equilibrates in your system it drops. You likely need to be "loaded" with enough B12 with enough B12 to fill stores put on maintenance. Also, multiple medications can affect B12.

Dropping B12: It would be most unusual for the level to drop from 600 to 140 in 2 months. I would suspect that one of those levels was inaccurate and would urge you to have your level rechecked to see if there was a lab error. Perhaps a hematologist would have more experience with markedly fluctuating B12 levels.