Remember that after ovulation, the follicle develops into the corpus luteum which will produce estrogen and progesterone. Both estrogen and progesterone acts on the hypothalamus and anterior pituitary to inhibit secretion of GnRH, LH and FSH. (negative feedback)
HcG (Human chorionic gonadotropin) does not increase the levels of FSH and LH. If fertilization occurs, the placenta will form which releases HcG. HcG acts on the corpus luteum to continue producing estrogen and progesterone. FYI: pregnancy tests detect levels of HcG because the placenta secretes this hormone and only when youre pregnant do you produce a placenta.
This is all done because, once you have fertilization, you would not want to produce FSH and LH. FSH (follicle stimulating hormone) --> Fertilization happened! Why develop more follicles?
Hope thats not all too confusing.