Infectious Mononucleosis (Epstein-Barr Virus Infection): This diagnosis is highly likely given the combination of fever, sore throat, and the specific mention of Epstein-Barr Virus (EBV) Ab. EBV infection, also known as infectious mononucleosis or "mono," commonly presents with these symptoms, along with fatigue and lymphadenopathy. The presence of epistaxis (nosebleed) could be related to the thrombocytopenia or vascular fragility sometimes seen in EBV infection.

Streptococcal Pharyngitis: This bacterial infection can cause fever and sore throat. While epistaxis is less commonly associated with streptococcal pharyngitis, it could occur, especially if there's significant inflammation or if the patient has a tendency towards nosebleeds.
Influenza: Influenza can present with fever, sore throat, and potentially epistaxis, especially if there's an associated sinus infection or if the patient has a pre-existing condition that predisposes to nosebleeds.
Common Cold: Although less likely to cause severe symptoms, a cold (rhinovirus infection) could potentially lead to these symptoms, especially if there's a significant nasal component that could lead to epistaxis.

Leukemia: Certain types of leukemia, such as acute lymphoblastic leukemia (ALL) or acute myeloid leukemia (AML), can present with fever, sore throat, and epistaxis due to thrombocytopenia or bone marrow failure. These conditions are life-threatening and require immediate diagnosis and treatment.
Aplastic Anemia: This condition, characterized by bone marrow failure, can lead to pancytopenia, including thrombocytopenia, which increases the risk of bleeding, such as epistaxis.
Hematological Disorders (e.g., Idiopathic Thrombocytopenic Purpura - ITP): Conditions that affect platelet count or function can lead to bleeding symptoms like epistaxis, along with other signs of bleeding or bruising.

Wegener's Granulomatosis (Granulomatosis with Polyangiitis): A rare autoimmune disorder that can cause a wide range of symptoms, including fever, sore throat, and epistaxis due to nasal and sinus involvement.
Lymphoma: Certain types of lymphoma can present with systemic symptoms like fever, sore throat, and potentially epistaxis, especially if there's significant lymphadenopathy or bone marrow involvement.
Vasculitis (e.g., Henoch-Schönlein Purpura): These conditions involve inflammation of the blood vessels and can lead to a variety of symptoms, including bleeding manifestations like epistaxis, along with skin purpura and joint pain.