Postnasal drip-induced pharyngitis: This condition is likely due to the patient's severe allergic rhinitis, which can cause excessive mucus production leading to postnasal drip. The constant irritation of the pharynx by the dripping mucus can cause pain and discomfort when swallowing.

Acid reflux (Gastroesophageal reflux disease, GERD): GERD can cause stomach acid to flow back into the esophagus, leading to pain and discomfort when swallowing. Allergic rhinitis can exacerbate GERD symptoms due to increased pressure and congestion in the nasal passages, which can lead to mouth breathing and increased pressure on the lower esophageal sphincter.
Tonsillitis: Inflammation of the tonsils can cause pain when swallowing, and allergic rhinitis can increase the risk of tonsillitis due to chronic nasal congestion and postnasal drip.
Pharyngitis (viral or bacterial): Pharyngitis can be caused by a viral or bacterial infection, and the symptoms can be exacerbated by allergic rhinitis.

Esophageal foreign body or obstruction: Although less likely, an esophageal foreign body or obstruction can cause severe pain when swallowing and is a medical emergency that requires prompt attention.
Esophageal perforation: A perforation in the esophagus can cause severe pain and is a life-threatening condition that requires immediate medical attention.
Cancer of the esophagus or pharynx: Although rare, cancer of the esophagus or pharynx can cause pain when swallowing and is a diagnosis that should not be missed.

Eosinophilic esophagitis: A rare condition characterized by an accumulation of eosinophils in the esophagus, which can cause pain and difficulty swallowing. Allergic rhinitis can be a contributing factor to this condition.
Pemphigus or other autoimmune disorders: Rare autoimmune disorders that can cause blistering and pain in the mucous membranes, including the esophagus and pharynx.