Hi. THANKS FOR YOUR QUERY. Read history about your child, constipation and fever , One thing is for sure - constipation can not cause fever; Pain in abdomen with fever can be due to the following reasons in a 3 year old child The most probable cause of pain in a child -Tummy tonsils- meaning enlargement of the lymph nodes of the abdomen. -Appendicitis- by default this has to be ruled out in every case of pain in -abdomen of a child. -Worms. The best diagnosis is a high resolution ultrasonography. some blood, urine and stool tests. A therapeutic trial with a course of an antibiotic, metronidazole and probiotics under the guidance of a pediatrician / Surgeon always helps to solve the problem and to get a diagnosis. Also given is a dose of medicines active against worms in intestine. I hope a consultation with a Pediatric Surgeon, investigations and a course of an antibiotic and metronidazole should solve the problem.