Baby acne?!

My little man has been diagnosed with newborn acne but is now into his third week and its starting to worry me. Has anyone else's baby had this? It is all over his face, ears, neck, head, back and chest and the heat isn't helping! The health visitor didn't seem too concerned about it but sent me to the GP last week who looked at him in a room with no windows and when not in natural daylight it actually doesn't look too bad! Just wondering how much longer I can expect it to last?! It looks so itchy and sore to me but have just been washing his face with cooled boiled water twice a day and then leaving it. Any advice?!