Constipation: Given the patient's history of using suppositories, Miralax, and stool softener, and the report of a small bowel movement, constipation is a likely cause of the abdominal pain. The pain radiating to the back could be referred pain from the abdominal region.

Gastroesophageal Reflux Disease (GERD): The worsening of pain throughout the day could be related to eating and acid reflux, which often worsens in the evening.
Peptic Ulcer Disease: Abdominal pain that worsens by the end of the day could be indicative of a peptic ulcer, especially if the patient has been experiencing increased acid production or has a history of NSAID use.
Cholecystitis: Although the patient denies fever, cholecystitis (inflammation of the gallbladder) can cause upper abdominal pain that radiates to the back, especially after eating.

Pancreatitis: This condition can cause severe abdominal pain radiating to the back and can be life-threatening if not promptly treated. The absence of fever or vomiting does not rule out pancreatitis.
Appendicitis: Although the pain is described as upper abdominal, appendicitis can sometimes present with atypical pain locations, especially if the appendix is retrocecal. The severity of pain and its progression are concerning for appendicitis.
Myocardial Infarction: In rare cases, myocardial infarction can present with epigastric pain or pain radiating to the back. Given the potential for severe consequences, it's crucial to consider this diagnosis, especially in patients with risk factors.

Splenic Infarct: This could cause severe upper left abdominal pain radiating to the back, but it is less common and usually associated with specific risk factors such as sickle cell disease or thrombophilic conditions.
Hepatic Infarct or Abscess: These conditions are rare and would typically present with additional symptoms such as fever or jaundice, but they cannot be entirely ruled out without further investigation.