Suggest Treatment For Penis Discomfort

my 5 years olds penis hurts every time before he needs to wee. The Gp pulled back his foreskin (which i had never done before) and told me to keep doing this every time he washes. After the Gp visit, my son's penis stings when he wees. Is this ok and how far back should i be pulling back his foreskin. At the moment, the tip of the head is visible and looks very red.