My 13 year old son has chronic abdominal pain w/many other symptoms, we've run every test under the sun to no avail. Should we see an endocrinologist?

Endocrinologist? If he has had all the appropriate gastrointestinal tests and exams, he may not have a structural problem. His problem may be functional sometimes caused by tissue oversensitvity or abnormal chemical signals between intestinal cells. Comparing activities/stresses with symptoms may uncover a psychological cause best treated by mental health specialists. May be more helpful than endocrinology.
See another peds doc. 13 Y.O.'s with chronic abdominal pains with "many other symptoms" may need another coach for a second opinion. I don't think the endocrinologist needs to be consulted yet. I would change peds docs and also consider a GI consult depending on the "many other symptoms" reported.