That’s how they start you on B12 jabs, frequent injections for I think two weeks, to get your levels up, then once every three months.
You should start to feel the benefit fairly soon, I doubt it’s the injections making you feel nauseous but I could be wrong.
B12 is absorbed at the very end of the small intestine, the terminal ilium, just before it joins the large intestine (colon) so I would think that because you’ve had most of your intestine removed you just don’t absorb it. I have Crohn’s disease and have a similar problem, wouldn’t matter how many B12 tables I took I’d never absorb it, so I have the jabs too.
Sometimes I feel quite awful and really tired just before the next one is due, sometimes I don’t. Once your level is sorted out you’ll look back and be amazed at the difference. Good luck x