Hi Sara,
You should check with your doctor's office because we each have unique situations. I am also on MMF and I didn't hold it the first time as there was no guidance at that point. The second shot I did. When it came time for the third my rheumy said not to hold it because I had too much disease activity. Most likely you won't need an appointment to find out, a call should suffice.
One thing to note since you are taking MMF, you may not get the same coverage from the vaccine as people not on it. The recommendation is to continue with precautions. When I brought up the issue my doctor had antibody tests done so we would have an idea where I stood.
Take care,
Lazylegs