After child birth, it takes time for the soft tissues to settle back to a baseline postpartum state. Every woman is different. Some women have more elasticity to their skin and muscle fascia - and "bounce back" closer to their pre-pregnancy form. Other women have less elasticity to the skin, and develop various amounts of skin laxity (or loose skin) or stretch marks. Muscle fascia weakness, especially the Abdominal muscles, can often remain after childbirth. This can cause mothers to have widened rectus muscles with a bulging abdomen and poor posture. This rectus diastasis (spread thin abdominal muscle fascia) can also magnify an existing hernia, or develop into an eventual hernia. I usually try to tell postpartum mothers to wait until they have stopped breast feeding, have returned close to their prepregnancy weight, and ideally are at least 6 months after childbirth - before considering which body contouring procedure to pursue. Everyone is different, and a consultation with an ABPS board certified plastic surgeon should be had at this time.
You are 8 months pregnant, you should be concentrating on prenatal and post natal care for the child and mother, not a big buttock.
You will need to breast feed, bond with your child , your child will need mother care for years.
You hormone levels are going to take a long time to settle, long time for the tissue to settle.