3 weeks after the encounter was a good time to check for gonorrhea, but not enough for the rest of STDs that can be transmitted through oral sex : syphilis and herpes. I would recommend you to test for those two as follows :
-6 weeks after the encounter for syphilis.
-3 months after the encounter, for herpes.
Nothing is pointing that the symptoms you are suffering are caused by a STD.
All the best.