Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your complain it seems that sore throat after having Oral sex can be most commonly due to bacterial infection secondary to improper maintenance of genital hygiene.. Sores at the back of tongue/ throat seems secondary to infection.. Sexually transmitted infection that occurs commonly are Chlamydia, Gonorrhea , Syphilis, Herpes etc can occur through Oral sex but has certain incubation period that is time duration between exposure to infection and appearance of symptoms of disease and as it is just 3 to 4 days chances of STD ate less and seems like common bacterial throat infection.. I would however advice that you should consult an Otolaryngologist and get evaluated and a thorough clinical evaluation and investigations like Throat swab culture can help in diagnosis and treatment can be done accordingly.. You can be advised to take a course of antibiotics, anti inflammatory painkiller, warm saline gargles and steam inhalation.. You can be advised to suck throat lozenges and chew a Vitamin C pellet.. Avoid spicy and chilled foods and drinks l plenty of water.. Gargle with numbing mouthwash can also relieve pain.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.