Baby ache?!? FTM and concerned

FTM and notice these on my son neck . He had baby acne( confirmed by his doctor) on his face and neck but it has come and gone on his face but seem to be getting worse on his neck .Now I no . I just purchase aquaphor to start putting on it. But any ideas on what it is .? Should I maybe go see his doctor .? He’s not bothered by it at all. He does have neck rolls could maybe it just be from milk that I don’t wipe up really good like I thought I was .