well my first thought that came to mind was appendicitis...but the time frame doesnt fit...what you could check into would be maybe a a pulled or strained muscle on the interior of the abdominal wall...i just recently pulled a muscle in my inguinal area...hurts like crazy...i thought it was appendicitis or something crazy turns out inguinal ligament got strained real bad and is causing shooting pains into my back and lower chest...takes about six to eight weeks to heal! similar to the symptoms you were talking about
Abdominal pain can be very hard to diagnose, but I'd ask about upper and lower endoscopy. Maybe the upper needs to be push enteroscopy to check below your stomach, if your insurance would go along with it.