I really need help

It is summer and my poor son keeps getting diaper rash. I change his diaper every hour and put strong diaper cream on him, it hurt me when I wash him and see that it is red down there and he is crying because he is in pain. I want to potty train him, but he still doesn't understand what the toilet is for and the idea of poo and pee. He is 2 years and 2 month old, he has speech delay. I don't know what to do. I leave him naked around the house to help with the rash. I just don't get it is there something I'm doing wrong? I change the diaper and found one that doesn't cause rash. I'm just at loss here I really need help. I tried to teach him by showing him his diaper when he poops and telling him to tell me when he need the bathroom. I tried taking him every 30 minutes to the toilet, he doesn't do anything and when he is off the toilet he pee. I really need help here he is my first child.