Uterus shrinking?

I’m little over one week postpartum, and my uterus is shrinking back to its normal size. The pain stop for maybe couple days but now it started again. My abdominal area is cramping so bad and my lower back and I feel like a little pain in my butt lol. Is this normal? 😅😅 this is my 4th pregnancy but I find it worse this pregnancy! When the pain does go away my abdominal area feels sore. Postpartum