Fibromyalgia: This condition is characterized by widespread musculoskeletal pain accompanied by fatigue, sleep, memory, and mood issues. It's a common cause of severe body pain involving joints and is often considered when other diagnoses are ruled out.

Rheumatoid Arthritis (RA): An autoimmune disorder that causes inflammation and pain in the joints. It's a common condition that fits the description of severe body pain involving joints, especially if the pain is symmetric and involves the hands and feet.
Osteoarthritis (OA): The most common type of arthritis, characterized by wear and tear on a joint, leading to pain and stiffness. While it typically affects one joint at a time, it can become widespread, causing severe body pain.
Lupus: A chronic autoimmune disease that can affect various parts of the body, including the joints, skin, kidneys, brain, and other organs. Joint pain and swelling are common symptoms.

Septic Arthritis: A medical emergency where a joint becomes infected, leading to severe pain, swelling, and potential destruction of the joint if not promptly treated.
Cancer (e.g., Multiple Myeloma, Metastatic Bone Disease): Certain types of cancer can cause severe body pain involving joints due to bone metastasis or direct involvement of the joints.
Acute Rheumatic Fever: A complication of untreated streptococcal infection, which can cause severe joint pain and has significant long-term cardiac implications if not treated.

Relapsing Polychondritis: A rare autoimmune disorder that causes inflammation of cartilage and connective tissue, leading to joint pain among other symptoms.
Sarcoidosis: A disease characterized by the growth of tiny collections of inflammatory cells (granulomas) in any part of the body, which can cause joint pain and swelling, though it's less common.
Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues, which can lead to joint hypermobility and pain.