Fibromyalgia: Given the family history of autoimmune diseases like scleroderma and lupus, and the presence of a positive CRP (indicating inflammation) but a negative ANA (which rules out lupus but not other autoimmune diseases), fibromyalgia is a plausible diagnosis. It's a condition characterized by widespread musculoskeletal pain accompanied by fatigue, sleep, memory, and mood issues, and it can sometimes be triggered by autoimmune diseases or have a familial predisposition.

Undifferentiated Connective Tissue Disease (UCTD): This condition presents with symptoms suggestive of a connective tissue disease (like lupus or scleroderma) but does not meet the full criteria for any one disease. The positive CRP and negative ANA, combined with a family history of autoimmune diseases, make UCTD a consideration.
Rheumatoid Arthritis (RA): Although RA typically presents with more specific joint symptoms and often has a positive rheumatoid factor or anti-CCP antibodies, early or seronegative forms could be considered, especially with a positive CRP indicating inflammation.
Mixed Connective Tissue Disease (MCTD): This disease combines features of lupus, scleroderma, and rheumatoid arthritis. A negative ANA does not rule out MCTD entirely, as some patients may have anti-U1 RNP antibodies instead.

Lupus with Negative ANA: Although less common, lupus can occasionally present with a negative ANA, especially early in the disease course. Given the family history, it's crucial not to miss this diagnosis.
Infectious Diseases (e.g., Endocarditis, Osteomyelitis): These conditions can present with systemic inflammation (positive CRP) and must be considered, especially if there are other symptoms like fever, heart murmurs, or localized pain.
Malignancy (e.g., Lymphoma): Certain cancers can cause systemic inflammation and mimic autoimmune diseases. A thorough evaluation is necessary to rule out malignancy, especially if other symptoms like weight loss or night sweats are present.

Sjögren's Syndrome: An autoimmune disorder that primarily affects the glands that produce tears and saliva, but can also have systemic manifestations. It might be considered, especially if there are symptoms of dry eyes or mouth.
Relapsing Polychondritis: A rare autoimmune disorder characterized by recurrent episodes of cartilage inflammation. It's less likely but should be considered if there are specific symptoms like ear or nose cartilage involvement.
Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. While not typically associated with a positive CRP, the familial aspect and potential for autoimmune overlap make it a rare consideration.