Gastroesophageal Reflux Disease (GERD) exacerbation: The patient is already on Prilosec for GERD and presents with epigastric pain and bloating, which are common symptoms of GERD exacerbation. The recent cessation of alcohol could also contribute to a change in symptoms or the perception of symptoms.

Peptic Ulcer Disease (PUD): Given the patient's history of GERD and the use of Prilosec, PUD is a possible diagnosis, especially if the patient has been non-adherent to medication or has an NSAID use that wasn't mentioned.
Functional Dyspepsia: This condition is characterized by recurrent upper abdominal pain or discomfort not exclusively relieved by defecation or associated with a change in stool frequency or form, which could fit the patient's symptoms of epigastric pain and bloating without other alarming features.
Irritable Bowel Syndrome (IBS): Although the patient does not report changes in bowel habits, some patients with IBS may present primarily with bloating and abdominal pain without significant alterations in bowel movements.

Myocardial Infarction: It's crucial to consider cardiac causes of chest pain, even if the pain is epigastric, especially in a smoker with a history of COPD, as these patients are at higher risk for cardiovascular disease. The absence of vomiting, diarrhea, or fever does not rule out MI.
Pulmonary Embolism: Although less likely given the nature of the pain, patients with COPD are at increased risk for pulmonary embolism, and epigastric pain can occasionally be a presenting symptom of a pulmonary issue, especially if it involves referred pain.
Gastric Cancer: While less common, gastric cancer can present with nonspecific symptoms such as epigastric pain and bloating, especially in older adults. A history of GERD and smoking increases the risk.

Pancreatitis: Although the patient does not have the typical severe abdominal pain radiating to the back or significant elevations in pancreatic enzymes mentioned, pancreatitis could still be considered, especially if there were recent alcohol use before quitting or other risk factors like gallstones or hypertriglyceridemia.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis could present with abdominal pain and bloating but usually are accompanied by changes in bowel habits, which this patient does not exhibit.
Gastric Volvulus or Other Gastric Obstructions: These are rare conditions that could cause epigastric pain and bloating but would likely have more acute presentations and possibly vomiting.