Thank you for you query on HealthCareMagic.
Does your son your diapers? In that case I would suggest that you stop using diapers for a few days and use cotton nappies. You can apply some bland cream or oil a couple of times.
In my practice I have observed a number of mothers to soak the cotton diapers in Savlon/Dettol
water before drying. This too can give rise to the rash/sores described by your. In case this is the practice being followed by you then please discontinue it.
I hope I have adressed your concerns to your satisfaction.
Wishing your son all the best........