Peroneal Nerve Injury or Compression: This condition can occur after an ankle sprain due to swelling or direct trauma to the peroneal nerve, leading to symptoms like numbness and heaviness in the leg. The fact that the symptoms are periodic suggests a possible intermittent compression or irritation of the nerve.

Deep Vein Thrombosis (DVT): Although less common in the context of an ankle sprain, DVT can cause leg heaviness and numbness. The negative X-ray does not rule out DVT, as it is typically diagnosed with ultrasound or other imaging modalities.
Compartment Syndrome: This is a condition where pressure within the muscle compartments increases, potentially causing nerve and muscle damage. It can present with pain, numbness, and heaviness, especially after trauma like an ankle sprain.
Muscle Strain or Contusion: Direct injury to the muscles of the leg during the ankle sprain could lead to localized pain, heaviness, and numbness due to inflammation and bruising.

Popliteal Artery Entrapment Syndrome: A rare condition where the popliteal artery is compressed, potentially leading to ischemic symptoms in the leg, including heaviness and numbness. It's crucial to consider this diagnosis due to its potential for serious complications if missed.
Spinal Stenosis or Lumbar Radiculopathy: Although less directly related to an ankle sprain, pre-existing spinal conditions could be exacerbated by altered gait or posture following the injury, leading to radiating symptoms into the leg.

Complex Regional Pain Syndrome (CRPS): A condition characterized by intense burning or aching pain in the affected limb, often accompanied by swelling, skin changes, and numbness. It can occur after trauma, including ankle sprains.
Neuropraxia or Axonotmesis: Specific types of nerve injuries that could result from the ankle sprain, leading to numbness and heaviness. These conditions might require specific management and could have a significant impact on recovery.