Still have symptoms after finishing Doxycycline and testing negative

Was feeling burning/itching, got tested and had chlamydia. Doc gave me 10 days of doxycycline, symptoms went away. I finished my pills on Thursday. I got a new gf during this time of treatment, and we started having sex (unprotected) after I finished treatment on the following Saturday/sunday. Immediately after, on Sunday, I started feeling the burning / inflamed feeling again in my urethra/penis.

I got retested the following Tuesday, my results came back negative for chlamydia.

It’s been over 11 days or so and I still have this burning feeling and it’s starting to drive me nuts. I took a urine culture test 2 days ago to see if it’s a UTI, but doc said that’s negative too.

Gf got tested and she is negative as well for everything.

Any idea what might be happening? Can I somehow still have chlamydia but it only showed negative because the doxycycline masked it? I don’t know what to do anymore.