Sorry to hear what you've been going through and I understand the worry it has caused. However, at this point you can be completely certain you do not have HIV and almost certainly no other STD.

First let's address HIV. Oral sex is low risk:  CDC estimates that if the insertive (penile) partner has HIV, the average risk to the oral partner from a single exposure is one chance in 10,000. That's equivalent to giving BJs to infected men once daily for 27 year before infection might be likely. Second, 4 days is too soon for onset of acute retroviral syndrome (ARS) symptoms; 8-10 days is the minimum. And perhaps most reassuring, your negative HIV test results definitely are conclusive. Their timing proves you don't have HIV and that HIV was not a possible cause of any of your symptoms.

Other STDs:  The main STD that causes overt exudative pharyngitis is gonorrhea, and even that is rare; 90% of oral gonorrhea is entirely without symptoms. Chlamydia rarely infects the throat and is not known to cause pharyngitis. So I'm not surprised those tests were negative. These tests are very reliable and you can be sure you had neither one. Syphilis is a theoretical risk, but is currently rare in heterosexual men and doesn't cause pharyngitis; the initial symptom (an open sore called a chancre) doesn't appear sooner than 10-14 days. Mononucleosis also can't start so soon, so I'm not surprised at that negative test result. 

In theory herpes could be considered. The timing is right, as is non-response to antibiotics. OTOH, having not had overt open sores in and around the mouth is evidence against it. But if such symptoms develop, testing for HSV might be a consideration.

At this point the cause of your pharyngitis probably will never be known. Probably it was viral (the exudative component actually is just a common in viral as bacterial), which fits with the long persistence of exudate despite antibiotic treatment. In theory, you could have acquired adenovirus from the oral sex; some strains cause urethral infection in men. (Did you by chance have any conjunctivitis -- i.e. pink eye? That often goes along with adenovirus.) Or any other virus, especially if your sexual encounter included kissing. Or it could just be a coincidence of catching a cold from day to day exposures to other people at around the time of the sexual encounter.

My bottom line:  You have no STD, probably just a coincidental viral infection. Most important, perhaps, is that you absolutely do not have HIV. I expect your symptoms to continue to improve -- all will be well. If this doesn't happen, further testing for mononucleosis might be considered. But I am confident you have nothing serious or dangerous for the long run.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

I am still experiencing periodic night sweats and muscle twitching/aching with a now itchy throat. I did forget to mention I was also blood tested for Syphillis at 6 weeks and it was negative. 

Are you saying that the blood test for mono could have been inaccurate at 4 days and could be positive now? 

Also, I don’t have an autoimmune disease but if I did would your advice change on conclusive testing for HIV? 

I appreciate you so much, as I know we all do on this forum. This has been debilitating. 

An infectious disease do also looked at my throat and said it doesn’t look like herpes and did not want to test further.

I'm afraid you're likely to never know whether your illness was acquired during the oral sex event (whether from the oral sex itself or other contact, like kissing) or from an entirely separate source, just a coincidence in time. But at this point I really don't think it should make any difference. As frustrating as that may be, and as debilitating as it has been, it sounds like things are improving and eventually you'll be entirely well, even if you're not quite there yet. Only now hearing you've seen an ID specialist, I'm guessing s/he had a similar assessment, right?

I also never recommend a necessity to go as long as your consultant recommends on HIV testing. I've never seen or heard of a case taking more than 6 weeks to for positive testing, no matter now high the risk. It has been over 20 years since I recommended that anyone needed testing later than 3 months after exposure or onset of symptoms.