Stretch marks on my butt!

Pre-pregnancy, I weighed 126. I'm 25 weeks and I weigh 141. I'm 5'3, and my body shape is little with big hips and a huge butt already. Today, my husband noticed red stretch marks on my inner butt cheeks. I have been putting bio oil on my stomach forever. I didn't think to put it on my ass. 🙄 It was huge before pregnancy. Ugh. Did this happen to anyone else?