I have had a long distance relationship with my gf for about a year now. Both 20 years old and white. We met in summer for 3 months and did a few things together then I left. During the 3 months we never had any issues. I met her for a few weeks after 8 months that we've been away. From that time on we were never involved with any other partners so pretty much you can call it a monogamous relationship. The issue here is that she gave me unprotected oral sex and a few days later I noticed a discharge coming from my penis and had exactly same symptoms as chlamydia/gonorrhea. After going to the doctor and doing a urine sample/blood tests, results came out negative to any STD. I received an Antibiotic shot in one go on the day of the visit and also prescribed azithromycin. Symptoms cleared and no I am confused what the problem is. What kind of tests does my gf need to go through in order to find what caused my infection? Does she have STD? During that week she told me she had a sore throat a few weeks before, Could it be just a bacterial problem?

Thanks for your time.
Please help me