Irritable Bowel Syndrome (IBS): The patient's symptoms of recurrent episodes of severe nausea, stomach cramping, pain around the belly button and rib cage area, and loose stools, especially occurring at night, are consistent with IBS. The lack of response to various treatments and the long-standing nature of the symptoms also support this diagnosis.

Gastroparesis: Delayed gastric emptying could explain the nighttime worsening of symptoms, nausea, and abdominal pain. The patient's trials of various anti-nausea medications without relief might suggest a motility issue.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis could present with abdominal pain, nausea, and loose stools. The absence of blood in the stool and the long history without significant weight loss or other systemic symptoms make this less likely but still a consideration.
Functional Dyspepsia: This condition involves recurring signs and symptoms of indigestion that have no obvious cause. Symptoms can include pain or discomfort in the upper abdomen, early satiety, and nausea, which overlap with the patient's complaints.

Appendicitis: Although the pain around the belly button is not typical for appendicitis (which usually presents with pain migrating to the lower right abdomen), any condition causing severe abdominal pain warrants consideration of appendicitis due to its potential for serious complications if missed.
Intestinal Obstruction: This is a medical emergency that could present with severe abdominal pain, nausea, vomiting, and changes in bowel habits. The patient's symptoms of severe abdominal cramping and loose stools could be indicative of a partial obstruction.
Pancreatitis: Abdominal pain, especially if radiating to the back, and nausea could be symptoms of pancreatitis. The absence of vomiting and the description of the pain do not strongly suggest pancreatitis, but it remains a critical diagnosis not to miss.

Cyclic Vomiting Syndrome (CVS): Characterized by recurrent, severe episodes of vomiting, this condition can also involve abdominal pain and nausea. The patient's symptoms do not perfectly align with CVS, given the absence of vomiting and the presence of loose stools, but it's a rare condition that could be considered.
Abdominal Migraine: This condition is more common in children but can occur in adults, presenting with recurrent episodes of severe abdominal pain, often accompanied by other migraine symptoms like headache or nausea. The patient's long history and specific symptoms could potentially fit this rare diagnosis.