Thanks for the query to ATD for an opinion.
With the history of oral sex,the lesion at the back of your throat typically indicates that you have had rough sex and your posterior pharyngeal wall has suffered contact injury which has caused the mucosal layer to abrade leaving behind a fiery red lesion which shows inflammation and is like to be painful as well.
If the std status of your partner is unknown then it would be advisable that you undergo a throat swab for culture to screen out STDs like gonorrhoea or chlamydia or it may be a simple strep infection.The diagnosis would be confirmed by swab test culture following which antibiotics may be started.
In the meantime you may practice saline warm water gargles thrice a day to help reduce the oedema and pain.
I hope I have answered your query in detail.
Wishing you good health,
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.