Heart Failure with Preserved Ejection Fraction (HFpEF): Given the patient's obesity, dyspnea on exertion, and bilateral lower extremity edema, HFpEF is a strong consideration. The normal echo does not rule out HFpEF, as the ejection fraction can be normal in this condition.

Nephrotic Syndrome: Resistant hypokalemia and bilateral lower extremity edema could suggest nephrotic syndrome, especially if the patient has significant proteinuria.
Chronic Kidney Disease (CKD): CKD can cause edema, dyspnea, and electrolyte imbalances, including hypokalemia, particularly in the context of obesity, which is a risk factor for CKD.
Hypertension: Uncontrolled hypertension can lead to heart failure, CKD, and electrolyte disturbances, making it a plausible diagnosis given the patient's presentation.

Pulmonary Embolism (PE): Although less likely given the chronic nature of the symptoms, PE can cause dyspnea on exertion and, in rare cases, lower extremity edema. It is crucial to consider PE due to its high mortality rate if missed.
Constrictive Pericarditis: This condition can mimic heart failure and cause edema and dyspnea. It is less common but critical to diagnose due to its potential for severe outcomes if untreated.
Lymphatic Obstruction: Conditions like lymphoma or filariasis can cause significant lower extremity edema. While less likely, these conditions have significant implications for treatment and prognosis.

Fabry Disease: A genetic disorder that can cause edema, dyspnea, and electrolyte imbalances due to systemic vascular and cardiac involvement.
Lipedema: A condition characterized by abnormal fat distribution in the lower extremities, leading to edema. It is more common in women and can be associated with obesity.
Primary Aldosteronism: A condition causing resistant hypokalemia due to excessive aldosterone production. While it primarily presents with hypertension, it could contribute to edema in the context of other cardiac or renal conditions.