Why do these things happen in the early am...

My 3 month old baby had a red spot about the size of a quarter on one cheek, that is warm to the touch. I noticed it showing up early afternoon at least, but not the warmth. I thought it was just a red cheek. He's acting fine, everything's normal, so I'm not going to rush to the ER but.... Anyone experience this with their baby? I'm not finding any super clear info online that is this specifically