Can I donate blood if i have a b-12 deficiency?

As to the vitamin B12, when you donate blood they ask you a series of questions and they test your blood.

None of the questions has to do with B12 level or intake.  You didn't say the name of the shots, but I don't think they were on the list of medicines that preclude you from donating.

But they do also test your blood to make sure you can spare enough of it.  B12 deficiency can cause a kind of anemia called megaloblastic anemia (info below).  If you're anemic they won't let you donate.

Sorry I don't know about the MS.  You can call the organization running the blood drive (it's often the Red Cross) and ask these questions in advance over the phone.

Thanks for donating blood.