hello concerned parent.
thanks for writing into hcm.
i have gone through your query and understand your concern.
In children,less than 3 bowel movements per week can be considered
constipation.
you havenot mentioned your son's height,but as per his age of 13 years,i would suggest 42-45kg to be an ideal weight for him.
So basically what i would suggest here are dietary changes first of all,give him adequate fibre in diet and balanced diet with whole grains, fruits and vegetables and plenty of fluids mainly water itself.
ask him not to resist the urge to defecate and postpone ,but train him to pass stools whenever he feels the urge.
Liquid paraffin 10ml thrice daily can be given for 5 days if he has less than 2 bowel movements a week.
i would also recommend a tablet
albendazole one time (and to be repeated after 6 months) and also digestive enzymes 10ml twice daily to help with digestion and promote weight gain.
hope this helps and clears your query.followup if needed.good day