Gastroesophageal Reflux Disease (GERD) or Functional Gastrointestinal Disorder: Given the symptoms of vomiting and constipation, which are common gastrointestinal complaints, a functional disorder or GERD could be the most straightforward explanation. These conditions are prevalent and can cause significant discomfort without necessarily indicating a more severe underlying disease like cancer.

Irritable Bowel Syndrome (IBS): This condition often presents with abdominal pain, changes in bowel habits (which could include constipation), and sometimes vomiting. It's a common cause of gastrointestinal symptoms and should be considered.
Gastroenteritis: An infection of the stomach and intestines, which can cause vomiting and constipation, among other symptoms. It's a common condition that could explain the patient's symptoms.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause a variety of gastrointestinal symptoms, including vomiting and changes in bowel habits. A family history of IBD or other autoimmune diseases might increase the likelihood.

Pancreatic Cancer: Given the family history, pancreatic cancer is a critical diagnosis not to miss. Although it might not be the first consideration for these symptoms, the family history elevates its importance. Pancreatic cancer can cause a range of symptoms, including gastrointestinal disturbances.
Gastrointestinal Obstruction: This is a condition where there is a blockage in the intestines that can cause severe vomiting and constipation. It's a medical emergency and must be ruled out promptly.
Neuroendocrine Tumors: These can arise in various parts of the body, including the pancreas, and might cause a range of symptoms depending on the hormone they secrete. A family history of pancreatic cancer could potentially increase the risk for other pancreatic disorders.

Cystic Fibrosis: Although more commonly diagnosed in childhood, cystic fibrosis can present in adults with gastrointestinal symptoms, including constipation and, less commonly, vomiting.
Amyloidosis: A condition characterized by the deposition of amyloid proteins in various tissues, which can lead to a wide range of symptoms, including gastrointestinal disturbances. It's rare but could be considered in the differential diagnosis, especially if other systemic symptoms are present.
VIPoma: A rare pancreatic tumor that secretes vasoactive intestinal peptide (VIP), leading to symptoms like profound diarrhea (which could be preceded by constipation), vomiting, and other systemic effects. The family history of pancreatic cancer makes this, although rare, a consideration.