There a std that can be mistaken for post nasal drip? the meds won't work, and it started after sex with another man. antibiotics/ steroids not help.

Possible: Candidal or herpetic esophagitis, gonorrhea and chylamidia can produce sore throat and cough which could present with sore throat and cough.

Gonorrhea can...: but then so can other bacteria and viruses, including non-STD. It could also be an allergy or other non-infectious cause. The only way to be able to eventually diagnose an infectious cause is to take specimens for testing, including cultures. If you got antibiotics you probably saw a doctor or mid-level provider. Did your provider take any specimens of throat or sputum before prescribing? See MD.

No: Post-nasal drips are not from STD. Get examined by your doctor.