What causes pain above the belly button?

Many possibilities: Pain around the belly button can result from a local issue, like a hernia, or from things arising from inside the abdomen, including inflammation of part of the GI tract, like the small bowel or appendix. Things like a viral gastroenteritis (aka "stomach flu"), bacterial infection from appendicitis, obstruction, pancreatitis, gastritis and ulcer disease can be causes. Best to get checked out.

Could be a hernia: Could be an umbilical or epigastric hernia. See you doctor for an exam.