Neither you nor your doctor should be retracting your son's foreskin at all. No one should except your son, himself, when the time comes. The foreskin is self-cleaning... just wipe the outside and be done. If you continue to forcibly retract him , you'll likely cause scarring which could cause him problems in the long run.
It will retract in its own time - generally, anytime between 3 years of age and puberty (or even beyond).