Hi,
Welcome to ehealthforum,
It can affect the normal hormonal pattern in your body that might cause alterations in your bleeding pattern. Consider visiting your doctor/gynecologist for a thorough evaluation and look for the cause behind your absent periods. If you had been sexually active since your last periods (and you are not on any form of birth control) then it could be suggestive of chances of pregnancy. If you get pregnant while being on Cellcept, then it could cause harm to baby, and you can even have early pregnancy loss.
Take care.