Go to the doctor and get a cream for it. Wish Idid earlier. I was lulucky enough to not get stretch marks but the rash scarred my tummy funnily enough. It was the lower part of my tummy amd I didn't go to the doctors to get cream until I was almost full term...but the cream got rid
I agree with Steph. Use pine tar soap.
You could also try an oatmeal bath.
Grandpa's Pine Tar Soap. You can get it on Amazon. Smells bad but gives relief