Welcome to the forum. Apologies for the slight delay in replying.
You describe a low risk exposure, for several reasons. First, in general the STD rates in Japan are lower than in most industrialized countries and syphilis is especially rare. (That you "don't see much difference" between heterosexual and gay male syphilis rates is a bit irrational. The fact is that syphilis is hundreds of times more common in gay men than in heterosexual men and women in the US and western Europe.)
Second, you describe a partner who is pretty careful, i.e. uses condoms regularly and gets tested for STDs -- and most people don't like about HIV status when asked directly. Third, you used a condom for insertive sex. Although genital contact without penetration ("grinding") isn't risk free, the chance of any STD is very low.
Had I been in your situation, I would have done exactly as you did -- i.e. would have had unprotected sex with my wife without fear of infecting her -- and I would not have sought testing or treatment for STDs. In my opinion, it's too bad your doctor talked you into treatment without testing. You may have saved a few yen, but you have made it impossible to ever know for certain whether you might have been infected, i.e. there is no testing that can ever be done to know whether you had acquired and were incubating gonorrhea, chlamydia, or syphilis.
But in any case, syphilis is not a concern at all. Even if you had been exposed, people are not infectious for at least 2-3 weeks after catching it. Gonorrhea and chlaymydia can be transmitted right away, but not syphilis.
Finally, the treatment you had -- 2 grams of azithromycin -- indeed is effective against all the STDs mentioned, as well as NGU.
At this point, my advice is to do your best to stop worrying about this. You truly had a low risk exposure and almost certainly were not infected, and your girlfriend is not at significant risk. I would advise you to let this go and move on.
Good luck-- HHH, MD
By the way, the japanese girl said she gets STD checks every three months. That increases the safe factor, however I am still somewhat concerned as it was a month ago after she was tested and due to language barrier info from her may not be too accurate.
Also the naked genital to genital grinding thing really concerns me .. seems its easy to get infection like herpes and syphilis.
The rising number on syphilis cases also worries me a lot although everyone says its far more common between men who have sex with men, but honestly I don't see much difference.
I am very worried feel bad that I am putting my girl friend at risk ..
Thank you doctors again ....
Noted before I replied; see above.