I have had abnominal pain for 30 hrs. It is constant. What could it be? It is in the middle of my belly. By my belly button

Need more info. Pain around the belly button can be several things some which are more or less serious. Deciding if it is emergent or urgent is important. If the pain is severe, associated with nausea, vomiting, fever, change in bowel habits like diarrhea and/or black or bloody stool you should be seen by provider today. If your pain has moved to the right lower part of belly go to er as you may have appendicitis.