The mom butt is when your buttocks get a little flatter or saggier than what it used to be before pregnancy. When looking from the side, your back goes straight down with no curves.
As you gain weight in pregnancy, that extra weight is unevenly distributed in your body. As a result, your pelvic posture changes, lengthening the glute muscles
Also, you are more likely to become less active the further along you get in your pregnancy. If you don't use it, you lose it
It's also important to know that the more you sit, the more you encourage the forward-tilted pelvis, glute inactivity, and increased low back pain.
It’s not uncommon for women to lose fat and muscle mass from breastfeeding, making their muscles look flabby. Your butt is one of the places it can happen
Unfortunately, your bum will not come back as soon as you stop breastfeeding. You have to work at it!