COP, if you can't take potassium supplements, are you allowed to eat a few more potassium rich foods?

If you can't take the potassium supplements, then just keep an eye on your body's reaction to the B12.

Once you've gotten your B12 under control, you can always look at taking a multivitamin at that point. You might feel a lot better after correcting your B12 that you feel like you don't need a multivitamin.