Nephrotic Syndrome: This condition is characterized by heavy proteinuria, hypoalbuminemia, and edema. The 5-pound weight gain and increased edema without a history of heart failure or shortness of breath (SOB) could be indicative of nephrotic syndrome, where the loss of albumin leads to decreased oncotic pressure and subsequent fluid retention.

Renal Failure: Acute or chronic renal failure can lead to fluid retention and edema due to the kidneys' inability to effectively remove fluid and waste from the body.
Liver Disease (Cirrhosis): Cirrhosis can cause edema and weight gain due to portal hypertension and hypoalbuminemia, leading to fluid accumulation in the body.
Hormonal Imbalance: Certain hormonal imbalances, such as those seen in hypothyroidism, can cause fluid retention and weight gain.

Deep Vein Thrombosis (DVT): Although less likely, DVT can cause unilateral edema and should not be missed due to its potential for severe complications, including pulmonary embolism.
Lymphedema: This condition, characterized by the abnormal collection of fluid in the interstitial tissue, can cause significant edema and should be considered, especially if the edema is unilateral.
Malignancy: Certain malignancies can cause edema through various mechanisms, including lymphatic obstruction or hypoalbuminemia due to liver metastasis.

Myxedema: A rare condition associated with hypothyroidism, characterized by non-pitting edema of the skin and subcutaneous tissues.
Idiopathic Edema: A rare condition of unknown cause, characterized by recurrent episodes of edema, often seen in women.
Fabry Disease: A rare genetic disorder that can cause edema among other systemic symptoms due to the accumulation of globotriaosylceramide in various tissues.