Allergic Rhinitis: The patient's symptoms of nasal congestion and cobblestoning, with some relief from antihistamines, strongly suggest allergic rhinitis. The recent move to a new farmhouse could expose the patient to new allergens, triggering or exacerbating symptoms.

Vasomotor Rhinitis: This non-allergic condition can cause similar symptoms to allergic rhinitis, including nasal congestion, but is not typically associated with cobblestoning. However, it's a consideration given the partial response to antihistamines.
Infectious Rhinitis: Although the patient has normal vitals, a viral or bacterial infection could still be present, causing nasal congestion. The absence of systemic symptoms like fever makes this less likely but still a consideration.
Environmental Irritant Exposure: The new farmhouse environment could expose the patient to irritants like dust, mold, or chemicals, leading to nasal symptoms.

Anaphylaxis: Although the patient's symptoms are currently mild and responsive to antihistamines, any sign of worsening or systemic involvement (e.g., difficulty breathing, rapid heartbeat, fall in blood pressure) could indicate anaphylaxis, a life-threatening condition requiring immediate intervention.
Nasal Tumor or Polyps: While less common, nasal tumors or polyps could cause nasal congestion and cobblestoning. These conditions would not respond to antihistamines and could lead to more serious complications if not addressed.

Eosinophilic Granulomatosis with Polyangiitis (Churg-Strauss Syndrome): A rare autoimmune condition that can cause nasal congestion among other systemic symptoms. It's less likely given the lack of other symptoms but should be considered if the patient does not respond to typical treatments.
Sarcoidosis: This condition can affect multiple parts of the body, including the nose, causing congestion and other symptoms. It's rare and would typically be associated with other systemic findings.