HIV is uncommon in sex workers in Australia, so you probably were not exposed at all. And you had condom protected sex. Minor contact with vaginal secretions carries no significant risk. You did not need HIV testing at all -- but your test results are reliable and prove you were not infected. To your specific questions:
1) I'm sure this is an accurate test. Lack of FDA approval only suggests that the manufacturer decided not to market that test in the United States.
2) This sort of exposure is free of HIV risk.
3,4) "is that true some people saying if just small amount of HIV virus get inside of your body then it take longer for our body to produce antibody?" No. That's an urban myth.
The window period for antibody is 6 weeks, not 3 months; see the thread linked below for more discussion.
"Is that melanoderm and Caucasian have stronger body then xanthoderm (me) that take shorter time to produce antibody?" No. I've never heard this before -- but it is ridiculous.
The 90% estimate of condom effectiveness takes into account many exposures over long periods of time, including times that condoms break or are improperly used. For any single vaginal or anal sex exposure, a properly used condom that doesn't break is virtually 100% effective in preventing HIV.
Australia's sexual health centres are the world's best network of STD/HIV clinics. If you remain concerned, stop testing yourself and visit your nearest SHC for high quality professional evaluation and advice. In the meantime, stop testing yourself and stop worrying about HIV from the exposures described above.
Here's the link to the thread about testing window periods:
http://www.medhelp.org/posts/show/1704700
Regards-- HHH, MD