What really happens to your body after birth?

I’m 17 and recently found out I got pregnant while on birth control!! And I have decided to keep the baby and this might sound silly but what really happens to your body after birth. Like a few of my friends have said my “vagina is going to be loose now” and my “boobs are gonna get saggy” but I want to hear from women that have had kids what actually happens downstairs and to your body in general?