There are many different possible causes of abdominal pain and I recommend that you see a gastroenterologist
. Without additional types of descriptions and without knowing your age the possibilities include many conditions. Since you are a diabetic, it could be gastroparesis, especially if you pain comes on about an hour after meals and is associated with vomiting. Stomach ulcers and gastritis (inflammation of the stomach) could be the source of your pain. If the pain is in the right lower side of your abdomen, appendicitis is a possibility. If the pain is on the left side, it could be diverticulitis
. If its in the lower part of your abdomen, other causes (depending on whether your are male or female) should be investigated. Depending on the nature of your symptoms, a simple abdominal x-ray, a CT scan of the abdomen, or an endoscopy might help in determining the cause of your pain.
While they are not always the best physician for you to see, I would consider in your case a consultation with a gastroenterologist. This type of doctor
specialize in disorders of the gastrointestinal tract. They may not be the right doctor for your condition (since the cause of your condition is not known), but they do see a log of cases of abdominal pain and thus would be good source of a next opinion. Good luck.