Severe stomach pain for my child help.

My child has been having severe stomach pain for last 4 days that comes and goes throughout the day. On day 1 he vomitted once and then he has not vomitted. We rushed to ER and gave painkiller injections. Stools are normal. No vomitting. Only stomach pain all day. Hard to sleep at night as well. Prior to this 2 weeks ago, he also had high fever for 8 days around 103 to 104 which kept fluctuating. This subsided 10 days before tummy pain began this Sunday. We ran all tests for all kinds of diseases and everything was normal. Blood culture also normal. Ultrasound also normal. Currently he's on lanzol, sucralfate and cyclopam but it's not helping at all. We saw so many hospitals and doctors but this pain isn't going.