Trochanteric Bursitis: This condition is characterized by inflammation of the bursa located on the outer aspect of the hip, which can cause pain that wraps around to the mid buttock area. The pain is typically non-radiating and worsens with activities such as sitting down and standing up, making it the most likely diagnosis given the symptoms.

Piriformis Syndrome: This condition occurs when the piriformis muscle irritates the sciatic nerve, leading to pain in the hip and buttock area. Although the pain can be non-radiating, it often has a component of sciatic nerve irritation, which may not perfectly match the described symptoms but remains a plausible explanation.
Gluteus Medius Tendinopathy: Inflammation or degeneration of the gluteus medius tendon can cause hip pain that may radiate to the buttock area. This condition is common in individuals with poor hip mechanics or those who have recently increased their physical activity.
Osteoarthritis of the Hip: Early stages of hip osteoarthritis can present with pain in the hip and buttock area, especially with weight-bearing activities like standing up from a seated position. However, the pain is often more localized to the groin area.

Avascular Necrosis (AVN) of the Femoral Head: Although less common, AVN is a serious condition that can present with hip pain, especially with weight-bearing activities. It is crucial to diagnose early to prevent further damage to the femoral head.
Infection (Septic Arthritis or Osteomyelitis): Infections in the hip joint or bone can cause severe pain, redness, and swelling. These conditions are medical emergencies requiring prompt diagnosis and treatment.
Tumor: Both benign and malignant tumors can cause hip pain. While rare, it is essential to consider this possibility, especially in patients with unexplained weight loss, night pain, or a history of cancer.

Stress Fracture: Stress fractures around the hip area can cause pain that worsens with activity. These are more common in athletes or individuals with osteoporosis.
Greater Trochanteric Pain Syndrome (GTPS): This condition involves pain over the greater trochanter due to a combination of gluteus medius and minimus tendinopathy, trochanteric bursitis, or external coxa saltans (snapping hip). While not as rare as some other conditions, it is less likely than trochanteric bursitis given the specific symptom profile.
Referred Pain from Lumbar Spine: Although the question specifies non-radiating pain, it's worth considering that some lumbar spine issues can refer pain to the hip area without radiating down the leg. However, this would typically be accompanied by other symptoms such as back pain or stiffness.