I don't know about Prep, but I was able to get a Rx for Doxycycline from my Primary Care Physician just by asking for it.  He is, of course, aware of my sexual activities, just as I hope your PCP is aware of yours.  He told me that taking a dose of Doxy, after questionable unprotected sex, is currently being recommended my the main stream medical establishment, due, in large part, to a nationwide outbreak of syphillis.