“Why do I get stomach cramps and diarrhea at night?”

I don't know how long it has been, but the night cramps and diarrhea may be due to food taken during the especially if it is not home cooked. It could be an infection.

There are many possible causes, so a lot more detail is needed before a diagnosis can be made. Some causes include irritable bowel, celiac disease, lactose intolerance, colitis, etc., but it's not possible to venture a guess unless more information is obtained. You should see a PCP or GI doc for a proper work-up. Go sooner rather than later if you have weight loss, blood in the stool, or anemia.