Gastroesophageal Reflux Disease (GERD): The patient's symptoms of epigastric pain radiating to the chest, triggered by eating ice cream (a common trigger for GERD), and relief of symptoms after receiving a GI cocktail (which often contains antacids or histamine-2 blockers) support this diagnosis. The absence of nausea, vomiting, diarrhea, or GI bleeding and the presence of mild bloating also align with GERD.

Peptic Ulcer Disease (PUD): Although the patient's symptoms are not classic for PUD (e.g., pain not consistently relieved by food or antacids), the epigastric pain and bloating could still suggest an ulcer, especially given the occasional use of ibuprofen, which can increase the risk of PUD.
Functional Dyspepsia: This condition is characterized by recurrent or persistent upper abdominal pain or discomfort not exclusively relieved by defecation or associated with a change in stool frequency or form. The patient's fluctuating pain intensity and absence of other GI symptoms could fit this diagnosis.
Irritable Bowel Syndrome (IBS): While IBS typically presents with altered bowel habits (which this patient does not have), some patients with IBS can have upper GI symptoms like bloating and abdominal pain, making it a consideration.

Myocardial Infarction or Acute Coronary Syndrome: Although the patient's ECG and troponin levels were normal, and his symptoms do not strongly suggest cardiac ischemia, it's crucial to consider cardiac causes of chest pain, especially given the potential for atypical presentations.
Pulmonary Embolism: This is another critical diagnosis to rule out, despite the normal chest X-ray and lack of typical symptoms like shortness of breath or tachypnea, due to its high mortality if missed.
Esophageal Spasm or Esophageal Rupture: These conditions can present with severe chest pain and are important to consider, especially if there's a history of forceful vomiting or other predisposing factors, which are not clearly present in this case.

Zollinger-Ellison Syndrome: A rare disorder characterized by excessive gastric acid secretion leading to severe peptic ulcers and diarrhea. The patient's symptoms do not strongly suggest this diagnosis, but it could be considered if more common causes are ruled out.
Gastric Cancer: Although extremely rare in a 29-year-old without significant risk factors, any persistent or unexplained GI symptoms warrant consideration of malignancy, especially if the patient does not respond to initial treatments for more common conditions.