Every diaper change my baby cries bloody murder 😢. He doesn't have a diaper rash but i notice and felt this hard lump on one side of his butt crack. What can this be? anyone?

Update:

The side became a bump with pus in it. I FaceTime with his pediatrician and told me to take him to the ER. I did. So diagnosis was perirectal abscess they couldn't tell me what causes that my baby didn't have a cut or any rashes and no fever. So they took blood , urine, numb the area then cut it to drain the abscess. My baby was warrior. I cried my heart out seeing him going through so much. Now he is doing so much better, the pain is way less he doesn't cry as much when changing his diaper. We still to go back to see the surgeon to make sure it's healing right. Just wanted to inform you mamas.