Gallbladder Disease: Given the presence of a gallbladder polyp, it's plausible that the patient's symptoms are related to gallbladder dysfunction. The polyp could be causing intermittent obstruction or inflammation, leading to upper abdominal pain and swelling. The absence of ascites and gas makes conditions like perforation or severe infection less likely, but gallbladder disease remains a strong candidate due to the direct correlation with the polyp.

Irritable Bowel Syndrome (IBS): Although IBS typically presents with bloating and abdominal pain, it can sometimes cause upper abdominal discomfort. The absence of gas and ascites does not rule out IBS, as it is a functional disorder that doesn't necessarily show abnormalities on imaging.
Functional Dyspepsia: This condition involves upper abdominal symptoms such as pain, bloating, and discomfort without evidence of organic disease. It could be a consideration given the upper abdominal pain and swelling, especially if the gallbladder polyp is not causing symptoms.
Gastroesophageal Reflux Disease (GERD): While GERD primarily causes heartburn and regurgitation, some patients may experience upper abdominal pain and bloating. The symptoms could be related to GERD, especially if there's an association with eating or lying down.

Pancreatic Cancer: Although less likely, pancreatic cancer can present with nonspecific symptoms such as abdominal pain, bloating, and weight loss. The presence of a gallbladder polyp does not exclude this diagnosis, and given the potential severity, it's crucial not to miss it.
Hepatic or Biliary Tract Cancer: Similar to pancreatic cancer, these conditions can have vague initial symptoms, including abdominal pain and swelling. The gallbladder polyp could be a coincidental finding, and these cancers must be considered to avoid a delayed diagnosis.
Peptic Ulcer Disease: Complicated peptic ulcers can cause severe abdominal pain and could potentially lead to swelling if there's significant inflammation. Although less likely given the absence of gas and ascites, it's a condition that requires prompt diagnosis to prevent serious complications.

Sclerosing Cholangitis: A chronic liver disease that leads to scarring and narrowing of the bile ducts, which could potentially cause upper abdominal pain and swelling. It's less common and typically associated with inflammatory bowel disease, but it remains a rare consideration.
Abdominal Lymphoma: Lymphoma involving the abdominal lymph nodes can cause nonspecific symptoms, including abdominal pain and swelling. It's a rare diagnosis but one that should be considered, especially if other diagnoses are ruled out and symptoms persist.