See a DR ASAP. Certain tumors of the pancreas can release insulin which can cause severe hunger and symptoms unless you eat, and could also cause pain.
I'm so sorry about all of this, but you have to stop eating long enough for the doctor to do the test! The longer you let this go, the worse it will get. If you are eating to ease the pain and this is why you can't stop, let him know this. He could put you in the hospital overnight and do the test the next morning. You need to find a way to make this test happen. Maybe get up very early the day before your test so that you can go to bed very early and have your test early the next morning? If you can sleep instead of eating, and you have them schedule your appt. early, you can do this. Let me know if this won't work and we'll figure something else out. Take care.