Toddler diaper rash

My son is 18 months old, last night at some point in his sleep, he had diarrhea and didn’t wake up until 6 am, now he has a pretty bad diaper rash not only on his bum, but on his private parts as well and it’s causing him quite a lot of discomfort. I’ve been using creams, changing often. He screams and stiffens his body in pain when I change him, he loves baths so I tried a Luke warm bath this morning and he cried and climbed out of the tub. It breaks my heart to see him in so much pain and I’m wondering if there’s anything I can do to make him more comfortable?