Gastroesophageal Reflux Disease (GERD) with possible exacerbation by marijuana use: The patient's history of abdominal issues since childhood, recent onset of vomiting that is temporarily relieved by Zofran (an antiemetic), and occasional heartburn suggest GERD. Marijuana use can exacerbate GERD symptoms.

Cyclic Vomiting Syndrome (CVS): Given the patient's history of abdominal issues and the cyclic nature of her vomiting, CVS is a possibility. CVS is characterized by recurrent episodes of severe vomiting lasting hours to days, with periods of normal health in between.
Irritable Bowel Syndrome (IBS): Although IBS typically presents with abdominal pain and altered bowel habits, some patients may experience nausea and vomiting. The patient's long history of abdominal issues could suggest IBS.
Food Poisoning or Gastroenteritis: The onset of symptoms after consuming a Burger King meal could suggest food poisoning or gastroenteritis, although the prolonged duration of symptoms makes this less likely.

Pregnancy-related complications (e.g., ectopic pregnancy, hyperemesis gravidarum): Although the initial pregnancy test was negative, it is crucial to consider the possibility of a false negative or a pregnancy that has developed since the test. These conditions can be life-threatening if not promptly diagnosed.
Appendicitis: Abdominal pain and vomiting can be symptoms of appendicitis, which requires urgent surgical attention.
Intestinal Obstruction: The patient's inability to keep down solids or liquids and infrequent bowel movements could indicate an intestinal obstruction, which is a medical emergency.

Gastroparesis: A condition characterized by delayed gastric emptying, which can cause nausea, vomiting, and abdominal bloating. It is less common but should be considered if other diagnoses are ruled out.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause chronic abdominal symptoms, including vomiting, although they are less likely given the acute onset in this case.
Neurological disorders (e.g., brain tumors, increased intracranial pressure): Rarely, vomiting can be a symptom of a neurological disorder. Although unlikely, these conditions are important to consider due to their potential severity.