Vaccines while TTC

So I went to the doctor for blood tests and a work up (preconception stuff) all the results were fairly good except I have low b12 (I don't eat a lot of meat) so I am taking a supplement now. The only other thing that snowed up is that my measles/mumps/rubella immunity came back as inconclusive. I know I was immunized, I have traveled the work where these diseases are still prevalent and have never gotten sick. However, my doctor wants me to have a booster... Okay so far no big deal EXCEPT the nurse tells me I can't have it if I am currently pregnant (I am in my TWW) and I can't get pregnant for a month after receiving it. This means of I didn't conceive this month (a Halloween baby I hope :)) then I would have to take a month off TTC. This is only our 4th (or 5th, the first one was odd) cycle and I am not ready to take a month off.... But if it's going to be dangerous for a baby then I guess I have to. Thoughts? Advice?