Doctors say the postpartum period starts after childbirth and usually lasts for up to 12 weeks after birth. You might have heard this time be referred to as the fourth trimester. By then, your uterus should be back to prepregnancy size. And following your postpartum checkup with your health care provider, most people are cleared for sexual activity and exercise, too. However, the time it takes to recover from labor and adjust to parenthood can be different for everyone, so go easy on yourself.