day 1-4 there is a drop in progesterone causing the uterus lining to break down
day 4-14 this stimulates release of FSH from the pituitary gland which stimulates the devlopment of the follicle in ovary
stimulates oestrogen production which inhibits FSH so no more follicles mature
oestrogen also builds up lining
day 14 stimulates LH which causes ovulation
day 14-28 progesterone is released , maintaining uterus lining in case of pregnancy
inhibits LH and FSH
if there is no pregnancy , progesterone levels drop , restarting the cycle