Has GI Pain, Diarrhea, Cough, Sore Throat, Fever, Vomiting. Urine Test Done. On Miralax. Help?

My son has had ongoing issues with his stomach. One week ago he started complaining of GI pain (Prior to the pain one week ago a couple of times in the week prior he stated he did not feel good). He eventually fell asleep and woke up the next day with a temp of 103. The fever continued at 104 or higher for 3 straight days. No other symptoms present like n/v, diarrhea, cough, sore throat etc. On Monday morning the fever broke and he vomited 1-2 times. He still continues to compain of abdominal pain and has seen 2 Docs during this whole process. CBC nl, strep neg, abdominal exam ruled out appendicitis. We are attempting to obtain urine sample. He has lost 1 1/2 lbs since January. The doc told me to try giving him Miralax 16 caps in 64 ounzes of juice. We started this protocol this morning and after 2 caps in 8 ounzes of juice he started holding his lower abdomen (below umbilicus) and said his tomach was hurting pretty bad and could not drink anymore. I have put in a call to the doc for direction. Do you have any suggestions. Is his pedicatrician missing something. Also, I failed to mention this abdominal pain has been ongoing since 5-6 months. In the past no fever but his past weekend it seems to be a directly connected with the fever. When his fever would spike that was when his GI pain was the worse. Please help me. I am very concerned about my son.