I Have A One Year Old Boy And I Noticed

I have a one year old boy and I noticed recently he started scratching at the very top of his butt in the back and lower back. He would pull the top of his pamper at the back down a little bit and scratch away. I notice there was some bumps, very small, some red from him scratching so much. Some of the skin was dry and there is scarring from some bumps I guess because there is a few dark spots were bumps were. I don't know what to use on it. I want the itchyness and bumps to go away.