Growing Pains: This is a common condition in adolescents, characterized by recurrent pain in the legs, typically in the thighs, calves, or behind the knees. The pain often occurs at night and can be bilateral. Given the patient's age and the presentation of thigh pain without other alarming symptoms or abnormal lab results, growing pains are a plausible explanation.

Muscle Strain: This could be due to overuse or injury from sports or physical activities. The patient's age and the fact that the CBC (complete blood count) is within normal limits (WNl) suggest that an infectious or inflammatory cause is less likely, making muscle strain a possible diagnosis.
Osgood-Schlatter Disease: This condition affects the upper tibia, causing knee pain, especially in adolescents involved in sports. While the primary complaint is thigh pain, Osgood-Schlatter disease could potentially refer pain to the thigh area.
Stress Fracture: Although less common in the thigh, stress fractures can occur, especially in athletes who participate in high-impact sports. The normal lab results do not rule out this possibility, especially if the patient has recently increased their physical activity.

Osteosarcoma: Although rare, osteosarcoma is a type of bone cancer that can present with pain in the affected bone, which could be the thigh. It's crucial to consider this diagnosis due to its severity and the need for early intervention.
Ewing's Sarcoma: Another type of bone cancer, Ewing's sarcoma can also present with localized bone pain and should be considered in the differential diagnosis due to its potential severity.
Infection (Osteomyelitis): While the CBC is normal, which might suggest against an infectious process, osteomyelitis (bone infection) can sometimes present with normal blood work early in the course of the disease. It's a critical diagnosis not to miss due to the potential for serious complications.

Hypervitaminosis A: Elevated levels of vitamin A can cause bone pain among other symptoms. However, this would be an unusual cause of thigh pain in a teenager without a history of excessive vitamin A intake.
Fibrous Dysplasia: A condition where normal bone is replaced with fibrous tissue, leading to weakened bones and potential for pain. It's a rare condition and might not be the first consideration but could be a possibility in the right clinical context.
Gaucher's Disease: A genetic disorder that can lead to bone pain among other systemic symptoms. It's rare and would typically present with other signs and symptoms beyond isolated thigh pain.