First of all, keep in mind that I am unable to diagnose you because I am unable to examine you, this forum is for educational purposes. The interferon beta and glatiramer acetate (another common MS med) are not immunosuppresents, and thus they CAN be given when Hep B vaccine (or any other) are given. The only restriction are for live attenutated vaccines (such as measles, mumps, rubella (MMR)), in a patient recieving immunosuppresent therapy such as IVIG, Steroids, mitoxantrone, azathioprine, methotrexate, cyclophosphamide.
On the question of does Hepatitis B vaccine cause MS or contribute to relapses, several recent studies 2001, 2003 have concluded that the answer is no.
So, by all means get vaccinated. I hope this was helpful.