The patient's complaint of pain only when laying on a particular area suggests a few possible causes. Here's a breakdown of potential diagnoses:

Single most likely diagnosis
- Bursitis: This condition, which involves inflammation of the fluid-filled sacs that cushion joints and reduce friction, can cause pain when pressure is applied to the affected area, such as when laying on it.
Other Likely diagnoses
- Soft tissue injury: A bruise, contusion, or strain in the affected area could cause pain when pressure is applied, such as when laying on it.
- Skin lesion or cyst: A skin lesion, such as a sebaceous cyst, or an infected cyst could cause localized pain, especially when pressure is applied.
Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Abdominal or pelvic tumor: Although less likely, a tumor in the abdominal or pelvic region could cause pain when laying on the affected side due to pressure on the tumor.
- Osteomyelitis or bone infection: An infection of the bone could cause localized pain, which may worsen with pressure or movement.
Rare diagnoses
- Ehlers-Danlos syndrome: A group of disorders that affect connective tissues, which could lead to skin and joint issues, including pain when laying on a particular area.
- Complex regional pain syndrome (CRPS): A chronic pain condition that can cause severe, burning pain in one limb, which may worsen with movement or pressure.