help for my son

My son has felt bad for a year and a half.  It started with Mono. in April, 2009 and has felt bad sense.  He has felt sick to his stomach, along with just feeling bad in general.  He doesn't throw up, or have diarrhea.  He doesn't sleep well.  He describes the feeling of a knot under his breast bone - which made me think of GERD.  When he eats, he feels full quickly and therefore doesn't eat much.  Since this started he hasn't eaten right and has lost down to 113 pounds.  He's 21 and is about 5'9".  He's had an upper endoscopy which showed ulcers or irritated places in his esophagus and stomach.  The gastro. dr. gave him Prevacid, which he's taken for months.  I thought that would be the end of it...but no, he continued to feel bad.  He then had an abdominal CT scan, with and without contrast.  My son was unable to drink as much of the contrast has he should have, but the results were normal.  The radiologist mentioned he could see some stool in the colon (which I guess is not usually seen in a CT scan).  I'm extremely worried.  He's SO thin, and feeling bad every day for 1 1/2 years is beginning to take a toll mentally.  He's pretty down.  His insurance has very low coverage or I'd just put him in the hospital.  Does anyone out there have any advice?