Plantar fasciitis or heel spur: This condition is characterized by pain and swelling in the heel, often without erythema. The hard nature of the swelling and the absence of back pain could suggest a localized issue such as plantar fasciitis, especially given the duration of symptoms. However, the diffuse pain in the thighs upon raising the left leg might suggest a referred pain or a more complex issue.

Achilles tendonitis or tendinosis: This condition could cause swelling and pain in the heel area, especially if the tendon is enlarged or hardened. The lack of erythema does not rule out this diagnosis, as chronic conditions may not always present with significant inflammation.
Bursitis: Inflammation of a bursa near the heel could cause localized swelling and pain. The absence of erythema and the hard nature of the swelling might suggest a chronic bursitis.
Stress fracture: Although less common, a stress fracture in the heel or calcaneus could cause localized pain and swelling. The diffuse pain in the thighs upon raising the leg could be related to compensatory mechanisms or referred pain.

Bone tumor (e.g., osteoid osteoma, osteosarcoma): Although rare, bone tumors can cause localized pain and swelling. The hard nature of the swelling and the absence of systemic symptoms do not rule out this possibility. It's crucial to consider this diagnosis to avoid missing a potentially life-threatening condition.
Infection (e.g., osteomyelitis): Chronic infection of the bone could cause localized swelling and pain without significant erythema, especially in the early or chronic stages. The absence of fever or systemic symptoms does not exclude this diagnosis.
Deep vein thrombosis (DVT): The diffuse pain in the thighs upon raising the leg could suggest a DVT, especially if there are underlying risk factors. Although the primary complaint is heel swelling, DVT is a critical diagnosis not to miss due to its potential for severe complications.

Erythromelalgia: A rare disorder characterized by burning pain, heat, and redness in the hands and feet. Although the question mentions no erythema, this condition can have variable presentations and could potentially cause heel swelling and pain.
Sarcoidosis: A systemic disease that can cause inflammation and swelling in various parts of the body, including the heels. It's a rare consideration but could be a differential in cases with systemic symptoms or multiple sites of involvement.