Nephrotic Syndrome: The patient's presentation with hematuria, significant proteinuria (5+ protein on UA), low albumin, and swelling of the lower limbs is highly suggestive of nephrotic syndrome. The absence of a history of chronic illnesses or drug use reduces the likelihood of secondary causes, pointing towards a primary glomerular disease.

Acute Glomerulonephritis: Given the patient's hypertension, hematuria, and proteinuria, acute glomerulonephritis is a plausible diagnosis. The elevated creatinine and BUN suggest impaired renal function, which can be seen in glomerulonephritis.
Chronic Kidney Disease (CKD): Although the patient does not have a history of chronic illnesses, the presence of hypertension and significant renal impairment (high creatinine and BUN) could indicate CKD, potentially with a superimposed acute injury.

Post-renal Obstruction: Although less likely given the lack of specific symptoms or history suggestive of obstruction, it is crucial not to miss this diagnosis due to its potential for severe consequences if left untreated. Obstruction could lead to renal failure, and the presence of hematuria and renal impairment warrants consideration.
Acute Interstitial Nephritis: This condition can present with renal impairment and could be considered, especially if there were any missed or undocumented drug exposures or infections. However, the significant proteinuria and hematuria are less typical for interstitial nephritis.

Acute Tubular Necrosis (ATN): While ATN can cause renal failure, it typically follows an ischemic event or toxin exposure. The patient's presentation lacks a clear antecedent cause for ATN, making it less likely.
Vasculitis or Systemic Lupus Erythematosus (SLE): These conditions can cause renal disease but are less common and would typically be accompanied by other systemic symptoms or findings not mentioned in the patient's history.