Could be baby acne- Milia- you know when your baby breaks out at 5 weeks old. Sometimes it happens when kid skin heals and is pushing out some dirt or impurities. Does he have a ped. appt. coming up? Or call the office- the receptionist can probably tell you whether to come in if you're really worried, or the doc can sometimes allay your fears over the phone.
My son (22 mos) recently had stitches on his face and when they healed, he also developed some white little bumps like white-heads along the scar. The ped. recommended rubbing them gently with baby shampoo when I washed his face at night. That was 3 weeks ago and they have gradually disappeared.