What Cause Itchy Rash On The Stomach?

Hello, I recently just had a baby. 13 days ago and for the past two days my stomach has been really itchy. Just under my belly button and goes down as far as the top of my pubic area. Due to scratching it it has become red and I had bumps on it. The only way to describe it is like a nettle sting rash. It seems to be an on going itch that cones and goes through the day. It's really itchy I've truer not scratching it but it gets super itchy.