Hi ! In the present scenario, I am not in favour of any laxatives without any history of constipation
. The ongoing situation for your son is for last few months with history of fever, and not a general healthy child. I think you should consult a general surgeon
for a physical examination of the child, who may suggest you a few investigations to start with like CBC, ESR, Widal test/Typhi dot test, LFT, serum amylase and lipase,urine rotine and culture sensitivity test. On the radiological side, he may consider an ultrasound of abdomen and plain x-ray of abdomen in upright posture. Few month old history of fever, and abdominal pain
suggests some kind of chronic infection and extra pulmonary tuberculosis
can not be ruled out, apart from a case of recurrent appendicitis
presently forming some adhesions in the intestinal tract. But please do not take these as frightening, but simply as possibilities which are treatable. So consult your doctor and do the best. Good luck.