Muscle Strain or Overuse Injury: This is the most likely diagnosis due to the nature of the pain described, which is often associated with physical activity or overexertion of the muscles in the quadriceps and piriformis areas.

Piriformis Syndrome: This condition occurs when the piriformis muscle, located in the buttock region, compresses or irritates the sciatic nerve, leading to pain in the buttocks and, sometimes, down the leg.
Quadriceps Tendinopathy: Inflammation or degeneration of the quadriceps tendon can cause pain in the front of the knee and thigh, consistent with the described symptoms.
Iliotibial (IT) Band Syndrome: Although more commonly associated with pain on the lateral aspect of the knee, IT band syndrome can sometimes refer pain to the quadriceps area due to its attachment points.

Deep Vein Thrombosis (DVT): While less common, DVT can present with severe leg pain and should be considered, especially if there are risk factors such as recent travel, surgery, or immobilization.
Compartment Syndrome: A medical emergency characterized by increased pressure within a muscle compartment, leading to severe pain, swelling, and potentially permanent damage if not promptly treated.
Neurological Conditions (e.g., Sciatica, Lumbar Radiculopathy): Conditions affecting the nerves in the lower back can cause radiating pain into the legs, including the areas described.

Tumor or Cyst: Rarely, a tumor or cyst in the soft tissues of the thigh or buttock can cause localized pain.
Infection (e.g., Abscess, Cellulitis): Infections in the soft tissues can cause severe pain, swelling, and redness, although these are typically accompanied by other symptoms such as fever and warmth of the skin.
Vascular Conditions (e.g., Peripheral Artery Disease): Conditions affecting blood flow to the legs can cause pain, especially with activity, though these are more common in older individuals with risk factors for vascular disease.