Hello,
Welcome to ehealthforum and thanks for writing
Sore thorat can be due to various reasons as infection,cold and flu,allergy etc and the most common cause is viral infection.But if the symptoms are present after oral intercouse then it could be indicative of any sexually transmitted disease as Pharyngeal Gonorrhoea,Chlamydia etc.
Kindly visit a Primary Physician for evaluation and avoid having oral intercourse until the diagnosis is confirmed.
Take care!