Clostridioides difficile infection (CDI): Given the patient's history of antibiotic use (Ceftriaxone and Metronidazole) and the persistence of diarrhea despite normalization of AKI and lack of growth on stool culture, CDI is a highly plausible diagnosis. Antibiotic-associated diarrhea is a common side effect, and CDI is a well-known complication of broad-spectrum antibiotic therapy.

Antibiotic-associated diarrhea not related to CDI: Other mechanisms of antibiotic-associated diarrhea, such as changes in gut flora, could be contributing to the patient's symptoms.
Inflammatory bowel disease (IBD) exacerbation: Although less likely given the acute onset and lack of prior history, an exacerbation of IBD (e.g., ulcerative colitis, Crohn's disease) could present with similar symptoms.
Viral gastroenteritis: Some viral infections can cause prolonged diarrhea, although the absence of other symptoms (e.g., vomiting, fever) and the lack of epidemic context make this less likely.

Cholera: Although rare in many parts of the world, cholera can cause profuse, watery diarrhea and is a critical diagnosis to consider due to its potential for severe dehydration and high mortality if not promptly treated.
Toxic megacolon: A life-threatening complication of inflammatory bowel disease or infectious colitis, characterized by significant colonic dilation, which could be masked by the patient's current symptoms and antibiotic treatment.

Microscopic colitis: A condition characterized by chronic, watery diarrhea, often without other symptoms, and diagnosed by colonoscopy and biopsy. It's less likely given the acute onset but could be considered if other diagnoses are ruled out.
Whipple's disease: A rare, systemic bacterial infection that can cause chronic diarrhea among other symptoms. It's an unlikely diagnosis given the acute presentation and lack of other systemic symptoms but should be considered in the differential diagnosis of chronic diarrhea of unknown origin.