Rash/spots on baby chest

[BSL23]

Baby is 5 weeks old and has a rash/spots on his chest. Took him to the doctors and they prescribed antibiotics cream and after 5 days it calmed down.
The last few days, it’s come back. Just wanted to what it might be. I’ve attached some pictures.

My son used to get a rash like that at the end of a cold etc and it went by itself after 3-4 days.

But at 5 wks old id be going back to the GP, just to be sure it wasnt anything more serious. If he is ok in himself and nappies are normal im sure its just a precaution, but still worth checking..