What Are The Red Itchy Bumps On My The Buttocks Of A Child?

My 2 1/2 year old son has red bumps on his upper buttocks. He is 39 inches tall 30 lbs. He had eczema when he was younger these bumps do not look like eczema at all. My son was on antibiotics for an ear infection but that was almost 2 months ago. I noticed them yesterday when he kept trying to put hand in his pants because they were botheing him. They are causing him pain, this morning he cried when I changed him. It does not look like a diaper rash. No fever. He wears underwear during the day and pull ups at night. I put A&D mixed with hydrocortizone cream on the bumps, it didn't seem to help much. What could this be? Should I bring him to the clinic?