I haven't been anemic since surgery, but I would get anemic quite often before when I had a lot of bleeding during Crohn's flare up's.
B12 is one of the water-soluable vitamins and isn't stored in the body. I'm thinking that any excess would be excreted in the urine, but I'd check with a doctor since some vitamins can mess up other prescriptions that you're taking.
I noticed that you have Crohn's. Just an FYI, it is quite common for Crohn's patients to be deficient in B12. You might want to have your doc check it out.