Ok a kid at 16 should not have ulcers!!!!!! Are you sure it is an ulcer and not GERD (gastro esophageal reflux disorder) AKA heartburn????? Have you been to a GI specialist?? Most ulcer now a days have been linked to a bacterial infection. But unfortunately the only way to truely diagnose an ulcer is by an endoscopic procedure. They are not too bad, they make ya sleppy, put a small video camera down your throat and take pics of your stomach.
But without getting into too much medical stuff here, goto the drug store ask a pharmacist what over the counter medications you can take and then goto the AOPA web site and see if they are allowed.
Hope this helps ya!!!