What Causes Abdominal Pain From The Navel To The Pubic Region?

My son age 10 years complained for abdominal pain starting from naval area proceeding to pubic region and settling to right side. I rushed to emergency due to fear of appendics and he went through various examinations which include CBC, Urine DR, X -Ray abdomen, & ultra sound lower abdomen. All test were found OK except TLC level was a little higher then normal. CBC was again performed after 15 days which showed further increase in TLC. Doctor checked him clinically and declared no appendics and diagnosed that pain is due to constipation. Now even after 20 days that pain is there it appears n disappears on unspecified intervals. There might be no pain for 2 or 3 days but again he will feel pain on right side without any reason. He is still having constipation and passes hard stool only once in morning. Please help be what is reason of the pain and what should in do to get him relief.