firstly, you need to go back to the doctor and get your actual test results. that way you can confirm whether it is an STD rather than a random bacterial infection.
Story time.
When I first started dating my last girlfriend we were having ALOT of sex (as you do). Lots of anal sex too with no condoms. About a week after I started seeing her I had an itchy rash start forming on my balls and dick. I started to get worried about it and went to the doctor. Now half a week before I went on my first date with my girlfriend I had a one night stand with another girl and we had unprotected sex. I was worried that I had caught an STD from this girl and that I had now probably given it to my girlfriend.
I went to a doctor and he said it looked like I had herpes. He did an STD test but said there was no point in testing for herpes as you can have the virus without showing any symptoms. I insisted that he tested me for it. Anyway, turns out I was free of all STDs and didn't have herpes. It was a bacterial infection from having unprotected anal sex (ie. from feces). I took a course of antibiotics and it went away.
Maybe something like this has happened to you. regardless, go get your test results so you can be sure what your dealing with