Hi there,
The test at 5 days is a bit early BUT{ (its a big but), you were never at any risk of gono or chlamydia because you used a condom - that creates an impassable barrier. I am really shocked the Dr gave you that medication with no indications for it. That is actually really bad practice as it contributes to the antibiotic resistance. But I digress.
You had a slight risk to syphilis and herpes. You already have herpes so scratch that. As you quite rightly said, syphilis is uncommon in developed countries and a symptom of that is NOT itching. It starts with a round painless sore called a chancre where the infection took hold. So you say you it from the oral exposure but you were wearing the condoms (which absolutely lowers the risk even more) it would be at the base of your penis.
In your case, I dont know what the issue is. Maybe anxiety to work with (maybe a different) doctor but im pretty confident is saying that this is NOT an STI :)