Help! Diaper rash and diarrhea :(

My LO has a pretty bad diaper rash on his bum and he is having such a hard time when I try to change him or clean him up. I can tell he's in pain when he is using the bathroom and when I change him. The difficult part is he also has a little diarrhea. I'm breastfeeding and he usually poops a little with every change but right now it's pretty wet. I had let him lie naked for a little while but he poops so often that it's difficult for his bum to dry out. I feel so bad. I'm putting desitin extra strength and A&D. Any other suggestions? He's just over a month and it breaks my heart to see him in so much pain while I'm changing him