Hi thanks for your question.
Your right ,Most probably you have developed pharyngitis
following oral sex.The swelling in neck are enlarged lymph node
due to pharyngitis and tonsilitis.Fever and other symptoms are also due tp pharyngitis.This pharyngitis and tonsilitis is STD or not can only be confirmed by physical examination and investigations.This infection could not be due to HIV infection as HIV has long incubation period
but can be ruled out only after test for HIV.I would suggest you to consult a physician who may be able to evaluate you for STD and may be able to treat your throat infection
Hope this answers your question.