Constant Abdominal Pain

My son is 16 years old. He has had constant low-level abdominal pain for the past 2 years or so. Every once in awhile, the pain will escalate forcing him to stay home from school. Normally, the excessive pain is in the morning when he wakes up to go to school. He does not have excessive pain when he sleeps in. This year, the excessive pain episodes have increased to where he is missing at least 1 day a week of school. His doctor thinks it might just be growing pains. He has grown almost 6 inches in the last 2 years. Although, that growth had slowed down when his pain started escalating. He has been bullied at school in past years, but nothing noticeable in the last 2 years. We have tried Lactaid for lactose intolerance, Prilosec for acid, Titralac for gas, Tums for acid/gas, Ranitidine for who knows what, and Miralax. We are now using Align, a daily probiotic supplement. Nothing seems to be helping. We are also using Dicyclomine (supposed to suppress abdominal pain) and it may be helping a little. He burps a lot but doesn't pass gas a lot. He doesn't have heartburn or reflux. He doesn't have diarrhea. He's not constipated. He's had a CT Scan (only found a slight enlarged liver); normal blood work and normal urine test. Does anyone have any idea to offer?