Chronic Urticaria: The patient's symptoms of a recurring rash that resembles urticaria, elevated histamine levels (though within normal range for chronic urticaria), and the absence of other specific autoimmune markers (e.g., ANA negative) point towards chronic urticaria as a primary consideration. The condition is characterized by the recurrence of wheals (hives) for more than 6 weeks, which aligns with the patient's symptom duration.

Systemic Lupus Erythematosus (SLE): Despite the ANA being negative, SLE can sometimes present with negative ANA, especially early in the disease course. The patient's joint pain, Raynaud-like symptoms, and elevated inflammatory markers (ESR and CRP) could suggest an autoimmune process like SLE.
Mixed Connective Tissue Disease (MCTD): This condition overlaps with SLE, scleroderma, and polymyositis/dermatomyositis, and can present with joint pain, Raynaud's phenomenon, and skin rashes. The elevated IgA levels could be relevant, though not specific.
Sjögren's Syndrome: This autoimmune disorder can cause skin rashes, joint pain, and elevated inflammatory markers. However, the absence of specific symptoms like dry eyes and mouth makes it less likely.

Vasculitis (e.g., Henoch-Schönlein Purpura): Although less likely given the clinical presentation, vasculitis can cause skin rashes, joint pain, and elevated inflammatory markers. It's crucial to consider due to its potential severity and the need for specific treatment.
Lymphoma: Certain types of lymphoma can present with skin manifestations, joint pain, and elevated inflammatory markers. The significantly elevated IgA level warrants consideration of this diagnosis, though it is less common.

Schnitzler Syndrome: A rare condition characterized by chronic urticaria, bone pain, joint pain, and elevated IgM levels (though IgA can be elevated in some cases). The presence of urticaria-like rash and joint pain, along with elevated IgA, makes this a consideration, albeit rare.
Ehlers-Danlos Syndrome (Hypermobile Type): This condition can present with skin manifestations, joint pain, and sometimes autoimmune features. However, the primary features of hypermobility and specific skin findings (e.g., hyperextensibility, poor wound healing) are not mentioned.

Chronic Urticaria: Treat with antihistamines, consider adding corticosteroids for acute exacerbations, or immunomodulators if refractory.
Autoimmune Workup: Further autoimmune testing (e.g., anti-Ro/SSA, anti-La/SSB for Sjögren's, anti-Scl-70 for scleroderma) if SLE or MCTD is suspected.
IgA Nephropathy or Other IgA-related Conditions: Consider if the elevated IgA level is persistent and other symptoms suggest renal involvement or other specific IgA-related diseases.
Skin Biopsy: If the rash does not respond to initial treatments or if vasculitis is suspected, a skin biopsy may be necessary for diagnosis.
Regular Follow-Up: Monitor the patient's condition closely, adjusting the treatment plan as necessary based on response and development of new symptoms.