Girls, hi everyone! We have such a problem with our little one, they'r…

Girls, hi everyone! We have such a problem with our little one, they're pooping constantly, and it's very frequent and watery, the stools are yellow, but so frequent that their diaper is already irritated, and there's also a rash on their back, could this be something anyone has experienced? The pediatrician says everything's fine. I've attached a photo.