Inflammatory Bowel Disease (IBD): The patient's symptoms of generalized abdominal discomfort, bloating, nausea, unintentional weight loss, night sweats, intermittent diarrhea, and intermittent blood in stool, along with a positive FOBT, suggest a chronic inflammatory condition of the bowel. The normal CT scan and ultrasound do not rule out IBD, as early or mild disease may not be visible on these imaging modalities.

Gastrointestinal Infection: Despite treatment for H. pylori, Amoebiasis, and Pentatrichomonas hominis, and a negative stool PCR, the possibility of a persistent or new gastrointestinal infection cannot be entirely excluded, especially given the patient's travel history and exposure to potentially contaminated food or water.
Irritable Bowel Syndrome (IBS): Some symptoms such as bloating, abdominal discomfort, and changes in bowel habits could be suggestive of IBS, although the presence of night sweats, weight loss, and blood in stool are less typical for IBS.
Cardiac Conditions: The patient's history of palpitations and a syncopal episode, along with an elevated LDH, may indicate an underlying cardiac issue that could contribute to or cause some of the symptoms, including night sweats due to anxiety or stress related to cardiac dysfunction.

Tuberculosis (TB): Although the IGRA was negative and stool Mycobacterium TB PCR was negative, TB can present in many ways, including gastrointestinal symptoms, and is a significant concern given the patient's travel history and potential exposure. TB can cause night sweats, weight loss, and abdominal symptoms.
Lymphoma: The elevated LDH and the presence of night sweats, weight loss, and intermittent diarrhea could suggest a lymphoproliferative disorder. Lymphoma can involve the gastrointestinal tract and cause a wide range of symptoms.
HIV/AIDS: Despite a non-reactive HIV screen, the possibility of a very early infection or a false-negative test cannot be entirely ruled out without further testing or clinical correlation, especially given the patient's symptoms of weight loss and night sweats.

Whipple's Disease: A rare, systemic bacterial infection that can cause malabsorption, weight loss, diarrhea, and arthralgias, among other symptoms. It is often diagnosed late due to its non-specific presentation.
Gastrointestinal Amyloidosis: A condition where amyloid deposits accumulate in the gastrointestinal tract, leading to symptoms like diarrhea, weight loss, and abdominal pain. It can be associated with systemic amyloidosis and other conditions.
Carcinoid Syndrome: Although rare, carcinoid tumors can produce serotonin and other substances, leading to symptoms like diarrhea, flushing, wheezing, and heart valve abnormalities. Night sweats can occur due to the systemic effects of the tumor or associated hormonal imbalances.