menstruation and ovulation

Bio teacher 教話即使無ovulation(排卵), 都會有Menstruation(M)
我唔係太明,,
如果無ovulation, 咪即係唔會有chance有BB
無BB, uterine lining就不用thicken for possible pregnancy
=='' 那何來menstruation...//

呀~ 如果ovulation時egg無受精....
egg是不是會死掉...呢??

請教下我XD