stretch marks on my butt?!

Okay😭 super sad moment right now. I was 120lbs pre pregnancy and am now I'm 30+1 and at 143lbs. No strecth marks on my stomach or anywhere, but after getting out of the shower today I noticed a ton of purple/pink marks on both cheeks! Whyyyyy. I used to have such toned glutes and I lost all muscle and mass in my butt since becoming pregnant.