Diaper rash HELP

My little man is one and he has a terrible rash. I noticed it Monday and started putting destin on it by Tuesday it was HORRIBLE so I gave him a bath and let him run naked for a bit Wednesday it was almost gone. This morning it still looked almost gone and tonight I went to change him and it’s Flared up again so I did an oatmeal bath and let him run nakey but it’s just horrible he doesn’t want to sit and doesn’t want a diaper on at all. He’s screaming off and on. I just need some advise. I did call the night nurse line at his ped office but Ive been waiting for a call back for over an hour! So any help while I wait is much appreciated